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Guidebook for Conducting Airport User Surveys (2009)

Chapter: Chapter 4 - Survey Design

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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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Suggested Citation:"Chapter 4 - Survey Design." National Academies of Sciences, Engineering, and Medicine. 2009. Guidebook for Conducting Airport User Surveys. Washington, DC: The National Academies Press. doi: 10.17226/14333.
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45 This chapter describes the process of designing a survey after the initial steps and planning deci- sions that were discussed in Chapter 2 have been completed. Each part of the design process needs to be given careful consideration, because the way in which each is addressed will affect the qual- ity of the results as well as the costs of performing the survey. Considerations that are specific to particular types of airport-user surveys are discussed in more detail in subsequent chapters, which should therefore be read in conjunction with this chapter in planning a survey of a particular type. 4.1 Survey Population The results of a survey represent a sample drawn from the larger population, although in some cases the sample may consist of the entire population (often referred to as a 100% sample or a census survey). This section addresses the need to clearly define the population of interest, including the characteristics of the population required for survey planning and where this infor- mation can be obtained. 4.1.1 Defining the Population of Interest The first step in any survey design is to define the target population for which information is to be collected. For example, the target population could be origin/destination passengers at the airport, in which case connecting passengers would be excluded, or all airline or airport-based employees using the airport terminal, in which case flight crews not based at the airport would be included. While the target population may seem self-evident at first, the exact definition will influence the survey methodology and sampling strategy and requires careful thought. The population available to be surveyed may differ from the desired target population, depending on the survey period and method used to conduct the survey. For example, the sur- vey sponsor may wish to obtain information on all air passengers using the airport throughout the year. Performing a survey over a relatively short period limits the available population to trav- elers during that period, whose characteristics may differ from those at other times of the year. Similarly, performing an Internet survey of airport employees limits the available population to those with Internet access. The limitations imposed when a survey is performed must be fully understood when inter- preting the results. When the characteristics of the target population change throughout the year, as they generally do for air passengers, there is no way to know whether a survey performed over a fairly short period will provide a reasonable representation of average annual conditions. If information on average annual conditions is desired, it will be necessary to perform the survey over a number of different periods throughout the year to account for seasonal variations. C H A P T E R 4 Survey Design

In some cases, the individual members of the target population can be identified prior to the survey. For example, it will generally be possible to obtain a list of all airport tenants and it may be possible to obtain a list of all airport-based employees. However, it will not be possible to iden- tify every air passenger using the airport during a specific period. In the case of area residents or businesses, while it may be possible to define the entire population, in practice it will usually not be feasible to assemble a comprehensive list. In cases where it is not possible to identify individual members of the population prior to the survey, it is often possible to obtain some information about the relevant characteristics of the population, although this information will not necessarily be organized in a readily usable for- mat and may require some additional research. Some of this information may be prospective, such as flight arrival and departure times and the aircraft types assigned to each flight that can be obtained from the Official Airline Guide or other sources of flight schedule information. Other information may be historical and require extrapolation to the period of the survey. For example, fairly detailed information on air passenger trips in the United States by airline and market is available from the Bureau of Transportation Statistics of the U.S. Department of Transportation, and there are generally similar sources of information in other countries. Design of an appropriate survey sampling plan (discussed in Section 4.2) requires a well- defined target population, as well as information on the size of the target population. The types of data that can be used to determine the size of the target population include the following: • Enplaned/deplaned air passengers for the period of the survey. • Aircraft movements by time of day and seat capacity, typically available from airport flight information systems, gate assignment systems or tower records. • Vehicle counts on airport roadways, typically collected using automatic traffic counters. • Parking exit counts and duration data from parking systems. • Curb activity counts. The above list is not exhaustive. The exact data required to determine the size of the target population for a survey will be a function of the goal of the survey, the target population, and the type of survey being conducted. Additional details on defining survey populations are included in the chapters devoted to each survey type. 4.1.2 Identifying Sources of Information In addition to information on the overall size of the survey population, assembly of informa- tion on the composition and characteristics of the population will generally be desirable. This information will enable development of a more detailed sampling plan, as well as provide an indi- cation of the extent to which the survey results correspond to the distribution of characteristics within the population. This in turn will allow appropriate weights to be assigned to the individual survey responses so that the survey results can be extrapolated to the population as a whole. In some cases, detailed data on the size or characteristics of the population may not be readily available. For example, an airport authority may not have traffic counts on the terminal roadways or may have no information on the number of air parties arriving at the airport by shared-ride van or using off-airport parking. It is increasingly common for airports to use auto- mated vehicle identification (AVI) systems to track the number of trips made by different classes of commercial vehicles, such as shared-ride vans or hotel shuttles. However, even in these cases information on the occupancy of those vehicles is generally not available. Smaller airports may have no idea how many such trips are made. Similarly, where airport employers provide park- ing for their employees, the airport operator may have no information on the number of park- ing permits that have been issued, much less the number of vehicles parked at the airport by those 46 Guidebook for Conducting Airport User Surveys

employees on a given day. While an airport operator will generally know how many parking per- mits it has issued to its own employees, it may not know how often they are used. Therefore, in planning a survey, one of the first steps is to decide what characteristics of the population are desirable to know in order to develop appropriate weighting factors and what data on these characteristics are already available. Where information on desired characteristics is not readily available, what would be involved in obtaining it? Answering this question may require some consultation with operational staff or external agencies. As it becomes clearer how much work would be required, a decision can be made whether the benefits of improving the survey weighting process justify the effort involved. 4.1.3 Determining Population Characteristics Although the total number of air passengers per month is generally known from airline reports and the total number of airport employees is known from employment records, the more rele- vant information is how the flow of passengers or employees varies by time of day or day of the week. Because the number of surveyed passengers in any hour or the work-shift patterns of sur- veyed employees may not correspond to the overall distribution of activity, it is desirable to know how passenger flows or employee shifts vary over the day and week. Some airports require airlines to report air passenger statistics for each flight. In this case it is fairly straightforward to assemble data on passenger flows by time of day, although adjustments will need to be made for connecting passengers, unless these are reported separately. In the more common situation, where airlines do not report passenger traffic at this level of detail, one approach is to analyze the distribution of seats on departing and arriving flights and make assumptions about load factors. Where passenger data at the level of individual flights are not routinely reported, it may be possible to obtain this level of information for the period of the survey from the airline departure desk or by counting boarding passengers. Data may also be available from the Transportation Security Administration on the hourly variation in the flow of people through the security screening checkpoints, which can be used to refine assumptions about the variation in airline load factors at different times during the week. Similarly, it may be possible to obtain information from airport employers on the number of their employees who will start their shift at different times throughout the week for the period of the survey. In the case of airport ground access modes used by air passengers and airport employees, it would be helpful to know how the use of the different modes varies over the week. In principle, detailed information on the number of parking exits by time, together with how long those vehi- cles have been parked, should be available from the parking revenue control system. However, at many airports this information is not readily extracted from the database, and some manual analy- sis of printouts or even a sample of parking tickets may be necessary. Information on the use of other modes, particularly drop-off and pick-up by private vehicle, is more difficult to obtain. Counts of vehicle trips may be available from AVI systems or trip fees paid by the operators, but these counts will not necessarily correspond to air passenger use, because of variation in air party size, more than one air party in a vehicle, and vehicles traveling to or from the airport without passengers (deadheading). It may be necessary to perform an occupancy survey to determine appropriate assumptions for the variation in vehicle occupancy over the week. These counts can be supplemented by installing traffic counters at strategic locations on the airport roadway during the period of the survey. In some cases, the survey sponsor may not even know the overall size of the target population. For example, if the target population is local area businesses, the total number may not be known to the airport operator. Some research may be necessary to obtain data from external sources, such as city and county business license records. Survey Design 47

48 Guidebook for Conducting Airport User Surveys While the effort required to assemble statistical information on the size and characteristics of the airport user population can be considerable, the information has other uses apart from survey design. Combining information on airport user characteristics with the survey data will produce a more integrated profile of airport activity. 4.2 Sampling Strategy and Plan 4.2.1 Determining Strategy After identifying the population to be surveyed and determining whether this population can be counted, the next step in the survey design is to determine whether a census or sample sur- vey should be used. Depending on the type of survey the following strategies and plans must be determined: • If a census survey is to be used, determine how each individual in the population will be contacted. • If a sample survey is to be used, determine: – The sampling method (i.e., random, clustering, stratification, etc.), taking into account the overall budget and the feasibility and efficiency of collecting data using each method. – The sampling plan (i.e., multi-stage sampling, choice of strata or clusters, methods of sam- pling within clusters). The sampling plan to be used is very dependent on the type of survey being conducted (see Chapters 5 through 10). – The sample size for the level of accuracy required. Whether a census or sample survey is used, steps for minimizing non-responses should be identified. Consideration should also be given to whether further analysis of individuals not responding is required and overall estimates adjusted. The sampling plan to be used is very dependent on the survey type being conducted and is covered in the chapter for each survey type (for example, see Section 5.3 for surveys of air passengers). 4.2.2 Minimizing Bias The two main sources of bias in airport user surveys and measures to reduce their occurrence follow: • Use of non-random sampling procedures. Bias can be reduced by the following measures: – Selecting an appropriate sampling method for the type of survey population, location, and time constraints. – Training interviewers in sampling techniques. – Supervising the interviewers. – Developing backup plans for unexpected events affecting the sampling process, such as delayed or cancelled flights. • Non-response of sampled individuals, as non-respondents can have significantly different characteristics from those responding. Response rates (also discussed in Section 4.8) can be improved by the following measures: – Choosing the survey location and time so that respondents have time available to respond. – Keeping the questionnaire short, as well as easy to understand and complete. – Using well-trained, experienced, and friendly staff to conduct interviews. – Using multilingual interviewer staff and questionnaires if appropriate. – Providing incentives, such as pens or coupons for free coffee. Incentives are generally not required for airport user surveys but can help if respondents are significantly inconvenienced.

Survey Design 49 Sampling of air passengers to survey can be particularly problematic because of their tran- sience. Passengers arriving late at the gate are typically under-represented and have a high non- response rate, while connecting passengers are often over-represented. Appropriate sampling methods are discussed in Sections 5.2 and 5.3. 4.3 Questionnaire Design and Structure The design and structure of the survey questionnaire, including the wording of individual questions, is crucial to the success of a survey. Issues to be considered include what information to request, the order in which the questions are asked, how much detail to try to obtain, and the amount of time that respondents can be expected to spend completing the survey. 4.3.1 Length As the amount of information to be obtained by a survey or the level of detail desired for the responses increases, so does the length of the questionnaire. Once the decision is made to incur the cost of performing a survey, there is often a strong desire to increase the amount of informa- tion it provides. However, increasing the length of the survey may increase the refusal rate and the number of incomplete responses, and also reduce the number of surveys that the field staff can perform in a given time period, thereby increasing the cost of the survey to obtain the same number of responses. There are a number of practical limitations on survey length. The most obvious is the time that respondents are willing to spend answering the questions. This length of time will depend in part on the circumstances. Someone completing a survey questionnaire in the comfort of their office or home will generally be willing to answer more questions, and in greater detail, than someone who is standing in a busy airport terminal and is anxious to catch a flight. The survey methodology may also impose limitations on survey length. If the survey question- naire is a printed form that is completed by hand, it should take up no more than two sides of a single sheet of paper. The text has to be large enough for respondents to read and the form has to provide enough space to write in the answers. 4.3.2 Response Options Survey questions fall into three broad types, based on the response options: • Numerical, in which respondents provide a numerical value, which could include dates and times. • Categorical, in which respondents choose among predefined alternatives. • Open-ended, in which respondents can answer in their own words. The results of open-ended questions are much more difficult to analyze, but they may provide richer information because the respondents are not forced to select from a limited number of categories. For many applications it is common to use a hybrid form, in which respondents are presented with a set of categorical responses, one of which is “Other” with an option for an open- ended response. This option allows common responses that were not covered by the categorical options to be assigned their own category code after the fact. Also “Other” responses that really should have been one of the defined categories can be recoded. However, adding a category after the survey based on the “Other” responses can result in an under-reporting of that category, because some respondents who would have selected that option if it had been presented chose a defined category instead. This occurrence is less of a

50 Guidebook for Conducting Airport User Surveys problem with an interview survey, where the respondents cannot see the defined categories when they answer the question, than with a self-completed survey. In addition to being easier to analyze, categorical questions have the advantage that they are generally quicker to answer, because they typically involve just checking a box. Also, because they present the respondent with a predefined set of possible responses, they encour- age the use of standardized terminology, yet may also trigger a response that would not otherwise have been mentioned. While this is true for self-completed questionnaires, there is a potential disconnect with interview surveys, where the respondent does not see all the options and the interviewer assigns the response provided to one of the defined categories. Different interviewers may handle a similar response in different ways. This phenomenon is called inter-rater reliability, and it can be a particular problem when asking about ground transportation modes, because different respondents may refer to the same mode in many different ways. One solution is to provide interviewers with printed cards that list the defined options, which can be shown to respondents to help them provide an appropriate response. Categorical questions and the responses obtained from them may include the following types of problems: • The respondent checks multiple boxes when asked to check only one. The wording should make it clear whether one or multiple boxes should be checked. This wording should not be part of the question and should stand out. Web-based surveys and those using electronic data collection devices (discussed in Section 4.9) eliminate this error. • A categorical response for “Not applicable” or “No opinion” is not provided where some such form of non-response is appropriate. When using a rating scale for opinions such as 1–5 or 1–7, be careful to word all the questions in a consistent way so that the highest number corresponds to the most positive opinion and 1 corresponds to the most negative opinion. Consideration should be given to including a comment box after each group of questions to allow respondents to note any clarifications or other relevant information. 4.3.3 Question Wording The wording of questions is critical to the success of a survey. Respondents who misunder- stand a question are not going to provide the desired information. Worse, it may not even be clear that they have given an answer to a different question from the one intended. Similarly, interviewers who misunderstand a question may miscode the response. Therefore, considerable effort should be devoted to developing clear and unambiguous questions. Consider the question “How far do you live from the nearest airport?” The question is asking how far in terms of what: miles? blocks? travel time? travel time by car or by transit? And what kind of airport is meant: the local general aviation airport? the nearest airport with scheduled passenger service? Getting from the general and vague to the specific is both necessary and difficult. Airports with years of experience conducting user surveys are still investigating possible refinements to their questions. Unfortunately, the easiest way to discover that a question is problematic is to look at the resulting data. Preventing this after-the-fact problem requires a serious commitment of time and effort to planning, thoughtful consideration of possible answers, and thorough testing of questions before the survey is deployed.

Survey Design 51 There are two broad categories of questions: • Factual questions. • Opinion questions. Factual questions ask for factual information that the respondent should be able to provide (such as how many bags they checked or how they got to the airport), while opinion questions seek the respondents’ views on an issue. Opinion questions present respondents with a range of options so they can select the one that best describes their opinion. This type of question may take the form of a statement, with the respondents being asked how strongly they agree or dis- agree. Satisfaction questions that explore the respondents’ satisfaction with particular facilities or services are a subcategory of opinion questions. Wording concerns with factual questions largely revolve around ensuring that the intent of the question is clear to the respondents and that the descriptions used for categorical questions are unambiguous. For example, difficulties can arise over local terminology that may not be familiar to visiting air passengers, such as the names of different ground transportation services (discussed further in Section 5.4). Question clarity is particularly important with self-completed questionnaires, where there is limited opportunity for respondents to clarify the intent of a ques- tion or ask how their response should be classified in terms of the response categories provided. The challenge with opinion questions is to ask the question in a way that allows for a meaning- ful answer. Such careful wording is particularly important with questions that ask respondents to indicate how likely they would be to use some proposed facility or service, or their satisfaction with some existing facility or service. Because the likelihood of using a facility or service depends on the circumstances affecting the decision, such questions have to be framed in terms of a specific situation, such as the trip that an air passenger is currently taking. Similarly, because satisfaction with a given facility or service is influenced by both expectations and the respondent’s experience with the use of the facility or service, customer satisfaction questions need to be worded in a way that allows these influences to be identified. 4.3.4 Question Order and Interview Flow At least four considerations affect the order in which the different questions are asked: • The most obvious consideration is where the answer to one question affects subsequent ques- tions. For example, it is important to determine whether an air passenger is starting a trip or connecting between flights before asking questions about the ground access trip to the airport. • A more subtle but equally important consideration is to introduce requests for information in a logical sequence. Asking survey respondents the type of place from which they began their trip to the airport gets them thinking about where they started their trip and leads naturally to questions about the location of that trip origin, such as the city or zip code. Earlier questions can also help clarify the intent of subsequent questions. Asking how many people are traveling together clarifies subsequent references to the travel party, such as how many bags the travel party checked. • A third consideration is to obtain as much key information as possible if there is a likelihood that the respondent will be unable to complete the survey. Asking those questions earlier in the survey makes it more likely that they will be answered. • The fourth consideration is that most surveys involve some branching that depends on the responses to earlier questions. These branches or skip patterns can request more detailed information for certain responses or omit questions that do not apply. In the case of printed questionnaires, these skip patterns should not be too complex, or respondents or interview- ers will have difficulty deciding where to go next in the questionnaire and may miss key

questions or attempt to answer questions that do not apply to them. The order of the ques- tions is one way to simplify the skip patterns. Branching is less of a concern with programma- ble hand-held electronic data collection devices, because the software handles the skips based on the responses to earlier questions. However, complexity can significantly increase the cost of the required programming. Another less technical suggestion is that the questionnaire should start with a question that is easy to answer and non-threatening, such as: “Did you travel to this airport by ground trans- portation to take this flight or are you connecting between flights?” This will help in getting the respondent’s cooperation for the survey. 4.3.5 Translations In the case of surveys where respondents may have limited facility with English (or with the primary language of the area where the survey is being performed, if this is not English), consid- eration should be given to providing the questionnaire in other languages. This situation arises at airports serving bilingual or multilingual areas or at international airports, as discussed fur- ther in Section 4.8.3. It is preferable to have the translation performed by a native speaker of the language in question, because there may be subtle issues of usage that could affect how the ques- tions are interpreted. It is also desirable to have the resulting translation reviewed by an aviation specialist with knowledge of the language to make sure that the translator has understood the intent of the questions. The decision as to whether translations are necessary or worth providing will depend on the proportion of the target population who may have difficulty completing a survey in English. If this falls within the anticipated confidence interval for the survey as a whole, as discussed in Section 3.2, it may not be worth incurring the cost of the translations in order to include these users in the survey. However, even in this situation there may be other reasons for including non-English-speaking airport users in the survey, such as gathering information about foreign tourists. There are usually practical limits to the number of different languages that the questionnaire can be translated into, and the choice of languages will depend on the composition of the target market. Because the field staff may not be fluent enough in any of these languages to explain the nature of the survey, ask the questions, or understand the responses, the translated versions will most likely have to be self-completed. If so, a brief addition to the questionnaire may be neces- sary to explain its purpose, which in turn may change the layout of the questionnaire. It may be helpful to use colored paper to help the field staff distinguish between the different versions of the questionnaire. 4.4 Expected Data Collection Rate Factors affecting the rate at which interviewers can collect responses include the following: • Questionnaire design—length, format, and types of questions. • Types of information collected—opinions usually take longer than current factual information. • Surveying method—intercept interview or self-completed. • Competency of interviewers—good interviewers can complete significantly more surveys. • Airport layout—time needed to move between gates or between terminals, considering likely congestion and the availability of moving walkways and inter-terminal transportation. • Refusal rates—affect the number of potential respondents who must be approached to obtain a completed response. 52 Guidebook for Conducting Airport User Surveys

Collection rates differ significantly depending on these factors, but a rough guide to the expected average response rate per hour per interviewer is as follows: • Intercept interviews: – 6-10 per hour for a 3-4 page survey with about 25 questions. – 10-15 per hour for a short questionnaire (10-15 questions). – 15-20 per hour for a very short questionnaire (5-10 questions) and introduction. • Self-completed: 25-40 per hour. These rates are applicable to situations where there are passengers available to interview, and they include an allowance for typical gaps between interviews but exclude breaks and inactive periods, such as between flights. Where all passengers on a flight are surveyed, experience indicates that responses are typ- ically received from 40% to 60% of passengers. The non-responding passengers are mostly those who • Arrive at the gate after the first boarding call. They either cannot be interviewed in the short time available or decline to participate as they are getting ready to board the flight. • Decline to participate because they are engaged in activities such as working, reading, or talking with others. For groundside surveys, refusal rates generally range from 5% to more than 30%, depending on the survey type and method, and the time of day. 4.5 Survey Logistics 4.5.1 The Importance of Logistics Both the survey quality and the physical well-being and mental attitude of the survey team will be directly affected, positively or negatively, by the amount of thought given to logistics. One of the principal challenges with air passenger surveys is that they are conducted in the physical environment of the airport terminal. Careful attention to survey logistics is therefore critical to a successful passenger survey. 4.5.2 Survey Implementation Team Of first importance is the survey team. In addition to the strong project manager recom- mended earlier, the survey implementation team needs a technical expert, a field manager, field supervisors, and interviewers. This structure applies whether the survey is conducted in person or by handing out questionnaires. • The technical expert is charged with addressing any deviations from the survey design and making the most scientifically appropriate choices when challenges arise. • The field manager oversees operations and serves as a liaison to the project manager. • The supervisors oversee the daily operations. • The interviewers either ask questions and record answers or hand out forms, answer questions, and collect completed questionnaires. Ideally, members of the survey team will be quick on their feet and effective problem-solvers. These characteristics will be helpful when things go wrong, which is likely to happen every day. Flights are cancelled or delayed. Interviewers do not show up or are late. Interviewers show up in inappropriate attire. Lines are too long for interviewers to get where they need to be when they Survey Design 53

54 Guidebook for Conducting Airport User Surveys need to be there. Gate personnel refuse access to survey staff. Passengers get annoyed or complain. Security breaches or weather shut down the entire operation. Labor disruptions hinder airport operations. The variety of things that can go wrong is essentially endless, and every problem requires a solution as quickly as possible. It is therefore critical that the survey team develop contingency plans for everything from a late-arriving interviewer through weather problems to special events that either cause havoc at the airport or skew the passenger profile. Survey teams that do not do this in advance are likely to find themselves scrambling madly on a daily basis. Table 4-1 lists some common problems and possible plans for dealing with them. These guide- lines are general and would have to be tailored to the specific situation. 4.5.3 Other Logistical Considerations Field Office Space Survey teams that do not plan for adequate, appropriately equipped, and accessible field office space are likely to see the quality of their work and results suffer as a result. The first considera- tion is where the space should be located: before or after security screening. This decision should be driven by what type of access will be most convenient to field staff and least disruptive to the airport. The space should also • Provide enough room for the field manager, field supervisors and interviewers to check in, check out, and meet (perhaps for announcements or some refresher training). It need not accommodate the entire team, although a space for training the entire team will need to be identified and reserved. • Have the necessary technology and equipment, including Internet access, electrical outlets if electronics will need to be charged, a photocopier and fax machine if needed by the team, and storage space for supplies and equipment. • Be private (not shared with others) and locked, both to prevent conflicts and for security reasons. Table 4-1. Representative problems and contingency plans. Potential Problem Possible Contingency Plan Target flight is delayed Prepare a list of alternate flights to survey in case selected flights cannot be surveyed as planned. If departure delay is greater than 30 minutes, survey alternate flight. If departure delay is less than 30 minutes, continue interviews until team is scheduled to move to next flight and leave one interviewer behind to continue until boarding starts then rejoin team at next flight. Target flight is cancelled Survey designated alternate flight Severe weather disrupts flight schedules Shift interview schedule by a designated amount of time to allow as many flights as possible to be surveyed in the planned sequence. Interviewers fail to show up or arrive late Reallocate available interviewers among teams to ensure that each team has the required minimum number of interviewers. Interviewer runs out of survey forms Record responses on an already used form in a different color. Airline suspends operation due to strike Survey designated alternate flights

Survey Design 55 Communications The best and easiest way for survey staff to communicate with one another (interviewer to supervisor, for example) is by cell phone or walkie-talkie. This eliminates the cumbersome use of courtesy phones (assuming there is a telephone in the field office that can be called from a courtesy phone) or the wasted time of walking around trying to find someone. Provisions need to be made for sufficient devices and for charging them as needed. Parking As airports are well aware, parking is expensive. Arrangements for parking for members of the survey team who are not on the airport’s staff need to be made well in advance so they are in place when the survey starts. Provisions also must be made for parking tags, vouchers, or validations for those working early or late shifts when airport managers are not available. If arrangements are made for off-site parking, the team will need to consider the extra time staff will need to get to the airport, both in terms of scheduling and in terms of wages. Weather Conditions If the survey is being conducted outdoors (such as a survey of meeters and greeters or one of drivers), plans should be made in case of inclement weather. In hot weather, it is important to provide water. In the cold or rain, provision needs to be made for shelter and possibly for extra breaks to “thaw out.” Material and Equipment Appendix C provides a checklist of supplies and equipment that will be required for the typ- ical air passenger survey. This list can be adjusted to meet each survey’s needs and circumstances. Scheduling of Interviewers At least two shifts per day will usually be necessary because of the long hours that airports operate. The staffing schedule should avoid staff being assigned to a late-night shift followed by an early-morning shift. The schedule should also allow enough time for staff to move between the different survey locations. 4.6 Selection and Training of Field Staff 4.6.1 Quality of Field Staff When hiring temporary staff, it is important to remember that generally “you get what you pay for.” The more the airport is willing to pay for interviewers, the higher the level of com- petence of the interviewers who will respond and, with careful selection of candidates, the higher the quality of data that will be collected. The length of the temporary commitment is also important. Trying to get competent and experienced interviewers for one or two weeks of work will be considerably more difficult than getting and keeping the same interviewers for two months. Dealing with a contractor for temporary staff can introduce a different dynamic. Some con- tractors will have a pool of experienced, quality interviewers, but others will have just as much difficulty finding and keeping interviewers as the survey sponsor would. However, there will be a mark-up associated with the contract. The competence of the interviewers is a function of the final rate of pay, not how much is paid for their services to the contractor. It may seem that a high labor rate should attract good interviewers, but it is the final wage being paid to the inter- viewer that will attract quality interviewers, not the rate listed by the contractor.

56 Guidebook for Conducting Airport User Surveys Qualities to look for when selecting interviewers include the following: • Professional and educational background. • Experience in conducting airport surveys. (Experience in conducting surveys at other transportation facilities can be a substitute.) • Presentable dress and appearance. • Motivated, driven to perform, and willing to take up a challenge. • Strong interpersonal skills, friendly and outgoing, and willing to approach people. • Able to understand what data are being collected, and why. • Willing to pay attention to detail to ensure good data are collected. • Able to cope with long periods standing and lots of walking. • Comfortable using electronic devices, if such devices are to be used. • Fluent in the desired language(s). • Able to obtain a security clearance. 4.6.2 Interviewer Training If interviewers are to be used to conduct the survey, they will need to be trained. Training considerations will probably apply primarily to intercept surveys; telephone surveys are likely to be conducted by a call center already staffed with trained interviewers. This section therefore focuses on training intercept interviewers. Training is not an area in which the survey team should be looking for cost savings. Although many factors contribute to the success or failure of an intercept survey, skilled interviewers are mission critical. In addition, there are so many unique aspects to airport surveys that the training session should be mandatory, even when interviewers have already been trained by an outside vendor. The technical expert and field manager are likely to be the persons providing the training, and all field supervisors should also attend. It is a good idea for the project manager to attend as well, because sometimes that person can answer questions no other team member can. In addition, the project manager can identify any areas where the training is insufficient and point these out to the trainer before it is too late. Training should always take place at the airport. This location will not only facilitate the air- port tour (discussed in the following subsection), but will also expose interviewers to the con- ditions in which they will be working. It is better for interviewers who are taken aback by the distances involved in getting from gate to gate, or who are surprised by the prices of the food in the airport concessions, to find out sooner rather than later. 4.6.3 Content of the Training Session A sample agenda for a training session is provided in Appendix D. This outline can be expanded, shortened, or modified to meet a survey’s particular needs. After introductions of the survey team and the interviewers, the training should begin with a dis- cussion of the purpose, goals, and objectives for the survey. Ideally, this should be considered in the context of actions to be taken and decisions to be made; enthusiasm for the project on the part of the project manager is also beneficial at this point. If people understand why they are doing what they are doing and how important it is, they are more likely to be motivated to do a good job. Given the difficulty of attracting well-qualified interviewers, par- ticularly for a fairly short duration, the best approach may be to retain a market research firm to provide the survey staff, prefer- ably a firm with extensive airport survey experience. Such firms will generally be able to call on inter- viewers that they have used for other projects or that they employ on an ongoing basis. They can be made responsible for scheduling the field staff and providing field supervision. They may also have interviewers working on other projects who can be assigned to the survey as needed to handle peak periods or replace absent interviewers. Interviewers who have a long-term working rela- tionship with a particular firm are also much less likely to quit unexpectedly.

Survey Design 57 Having spent some time on “what’s in it for the survey sponsor,” the next part of the training should be devoted to “what’s in it for the interviewers.” People are always eager to learn about such basics as work hours and days, shifts, pay rates, and the like. Once they know what they are going to get out of participating in the survey, they will be more likely to pay close attention to what follows. The next part of the training should deal with expectations, including everything from pro- ductivity and quality to behavior, attire, and grooming. People need to know what the rules are, so they can put what they are supposed to do into the appropriate context. The next part of the training is typically devoted to basic interviewing skills. (The Bibliography lists some useful interviewer training manuals developed by the Council for Marketing and Opinion Research and Marketing Research Association.) Even if the project is being staffed with previously trained and experienced interviewers, it is wise to include this topic in the training by labeling it as a review. The quality of interviewer training varies considerably from firm to firm, and it is possible that the survey team will have higher standards than the firm from which the interviewers are drawn. After the interviewers understand the requirements of the job, it is time to go over the specifics. In this part of the training session, the questionnaire should be reviewed question by question. Any questions that could prove challenging for interviewers to ask or for respondents to answer should receive special attention. After the questionnaire has been reviewed, the use of devices that will be utilized in the survey (such as electronic data collection devices or laptops) should be taught. A tour of any airport facilities or services that are referenced in the survey, whether passenger amenities or ground transportation services, should also be included. This tour will also orient staff to the layout of the airport and the ways to get from one place to another. By the end of this part of the training, interviewers should know exactly how to conduct the survey. The final step is to have them practice, first by interviewing one another and then by con- ducting practice interviews with passengers or other target respondents. The results from the lat- ter should be reviewed by supervisors to ensure that they are accurate and complete before the interviewers are released to conduct actual interviews. 4.6.4 Duration of Training If the interviewing team is focused, it is possible to conduct an acceptable training session in a day, and a one-day training session appears to be the general practice. There is, however, a large amount of material to master, even for experienced interviewers, and fatigue can be a problem. In an ideal world, training would probably be spread over two days, with perhaps six hours of instruction and practice per day. While two days may seem costly, the expense could well be off- set by increased efficiency and accuracy of the interviewers during the actual survey, particularly during the first few days. Having interviewers familiarize themselves with the questions and sur- vey procedures during the actual survey not only reduces the survey completion rate (increasing the cost per completed survey) but also runs the risk of generating poor quality data until the interviewers gain experience. 4.6.5 Coaching and Retraining Even the best training session is not foolproof, and even a highly competent interviewer can fail to grasp an important point. It is therefore extremely important that everyone’s work be checked on a daily basis, particularly during the first few days of the project. Later work can often be spot-checked, but early work should be reviewed constantly.

58 Guidebook for Conducting Airport User Surveys It may then be necessary to take corrective action, either by coaching an interviewer who missed something during training or by retraining the entire group if the trainer failed to con- vey a point well enough. The survey planning team would be wise to budget for both of these occurrences, particularly if the questionnaires or procedures are complicated or difficult. It is also important either to train backup interviewers, who may or may not be deployed, or to provide for a second training session for new hires if people need to be replaced. As it is diffi- cult to find people who are willing to be trained without any assurance that they will have the opportunity to participate in the survey, the latter approach is more typical. However, a second training session can present scheduling difficulties because attrition of the trained interviewers can occur throughout the survey. Another problem arises with recruiting and training additional interviewers at short notice if they have to be issued with security badges, because this process can be quite time-consuming. Therefore, it may be better to recruit and train enough interview- ers at the start of the survey to allow for some attrition, and adjust the length of the survey period and the hours worked by each interviewer to manage the attrition that actually occurs. Finally, it is important to note that when mistakes happen, the decision about whether to retain and tabulate work that is imperfect is both a research and a policy decision. The research decision has to do with the necessity of having enough interviews to achieve the desired statistical preci- sion and power; the policy decision has to do with the importance of a given piece of information. It is also important to consider just how imperfect less than “perfect” work really is. 4.7 Pre-Tests and Pilot Tests Pre-tests of questionnaires and pilot tests of survey procedures provide an opportunity to identify any problems with question wording or other aspects of the questionnaire as well as the planned arrangements for performing the survey. Such tests allow corrections or adjustments to be made before the main data collection effort. 4.7.1 Pre-Test of Questionnaires The goal of a pre-test of the questionnaire is to make sure the survey questions can be asked easily by the interviewers, are clear to the respondents, and produce the desired information. Pre- tests also provide an opportunity to identify unanticipated responses or situations and to adjust the question response categories or the survey script as necessary. An initial pre-test may be performed on a convenient group of people who were not involved in developing the instrument, such as staff of the survey sponsor. However, while this may help improve the question wording and identify unanticipated responses that require changes to the question response categories, it is not a truly representative test of the questionnaire. It should be followed by a pre-test involving a sample of the intended respondents of the survey, per- formed in the same way as planned for the survey itself. This pre-test will increase the chances of identifying unanticipated responses or situations. The questionnaire designers should be involved in conducting the pre-test, because they will be able to identify unanticipated responses or any misunderstanding of the intent of a question better than someone who was not involved in the development of the questions. The results of the pre-test should be subject to careful analysis to identify any apparent difficul- ties with the question wording or survey flow, such as missing or incomplete answers, illogical responses, or incorrect skips. In particular, responses of “Other” to categorical questions, where the respondent has provided an explanation, should be examined to identify any misunderstanding of the categories or commonly occurring responses that should be added to the designated categories.

If electronic data collection devices are to be used in the survey, the programming needs to be thoroughly tested and debugged before the pre-test, or the validity of the pre-test may be com- promised by errors in the programming. A rigorous testing plan for the software should be included in the project schedule. This program testing, done by people other than the program- mers, will attempt to ensure that all possible response options and question branches are tested. This can be quite time-consuming and can be facilitated by preparing a set of response scripts that test all possible branches from each question. These test scripts ensure that certain response options are not overlooked, and can also be used to check that changes made to fix any problems have not affected other parts of the program. The survey schedule should allow enough time to adequately test the programming and make any needed revisions before the first pre-test. 4.7.2 Pilot Test of Survey Procedures The primary purpose of a pilot test of survey procedures is to identify any problems with the planned approach to conducting the survey and to refine the estimates of the number of field staff required. Because a pilot test typically involves performing the survey on a representative sample of potential respondents, it presents an opportunity to conduct a pre-test of the survey questionnaire, and the two tests are often combined. Other objectives of a survey pilot test include the following: • Testing the survey sampling strategy. • Validating the sampling plan. • Identifying problems with survey logistics. • Checking the data quality. Feedback from the pilot test should include both field observations by supervisory staff and issues reported by field staff in debriefing sessions, supplemented by an analysis of the survey responses collected. In the case of interview surveys, noting the start and end time on each response will enable this analysis to examine the average time to perform a survey as well as the interval between ending one interview and starting the next. This will provide information on the amount of time spent waiting for subjects to become available to be interviewed as well as the time required to move between locations. Field staff should also note refusals to participate and record the reason where given or apparent, such as a language barrier or cell phone conversation. The pilot test results should be compared to the expected number of responses from the sampling plan. This comparison may require collecting data on the potential number of respondents, such as the number of passengers on flights surveyed in airline gate lounges. The results should be exam- ined for data quality, including missing or incomplete information, apparently illogical or incon- sistent responses, or difficulty interpreting free-text write-in answers. Where addresses or other location data are collected, these should be examined to ensure that the location can be identified. While this analysis addresses many of the same issues as the survey pre-test, it focuses on the conduct of the survey rather than the design of the questionnaire. Results of the pilot test analy- sis can be used to identify issues requiring particular attention in training field staff for the data collection phase. 4.7.3 Scheduling of Pre-Tests and Pilot Tests Pre-tests and pilot tests should be performed far enough in advance of survey data collection that there is time to adequately analyze the results and resolve any issues, as well as perform any additional testing required. This process is likely to require several weeks to do well. Any changes to the questionnaire have to be finalized before the forms are printed for the data collection phase Survey Design 59

60 Guidebook for Conducting Airport User Surveys and may involve reprogramming electronic data collection devices, if these are used, which will also take time. Therefore, it is prudent to schedule the pre-test and pilot test at least a month before the main data collection. The exact amount of lead time must be carefully considered in the light of the time required for the intermediate steps, which will vary from survey to survey. 4.7.4 Quantity of Pre-Tests and Pilot Tests In general, one questionnaire pre-test and one pilot test of survey procedures will be sufficient. However, if the tests reveal problems that require significant changes to the questionnaire or pro- cedures, it may be desirable to perform a second pilot test to verify that the changes have suc- cessfully resolved the problems. When a second pilot test is not performed, the experience and results of the first day or two of the main data collection period should be closely scrutinized to ensure that any changes have produced the intended effects. 4.8 Maximizing Response Rates The willingness of potential survey respondents to participate in an airport user survey varies with the survey method and type of survey. Air passengers are generally cooperative, if they have the time. The response rates for other types of surveys, such as surveys of airport employees or tenants, can be improved by the way the initial contact is undertaken and the justification given for requesting the information. 4.8.1 Techniques that Improve Response Rates Intercept Interview Surveys Response rates to intercept interview surveys can be improved by the way the initial request is communicated. The quality, experience, and training of interviewers can significantly influ- ence response rates. Survey personnel should be clearly identified as performing an officially approved function by wearing identification badges (these will be necessary anyway if the sur- vey is being performed in the secure part of the airport terminal) and professional attire. It is helpful if survey personnel wear distinctive clothing that identifies them as performing a survey, such as vests or aprons marked “Airport Survey” or similar wording and the name of the survey organization. Clear identification will • Assure potential respondents that this is an officially sanctioned activity. • Help prevent airport, airline, or security staff from becoming suspicious about why the sur- vey staff are approaching people. • Simplify the initial explanation when the potential respondent is approached. High-visibility safety vests add to the safety of interviewers in groundside locations where vehi- cles and pedestrians mix. Vests and aprons can also be designed with large pockets to make it easy to carry forms, pens and so on. Survey staff should be trained to follow a standard introductory script that explains the pur- pose of the survey, which organization or organizations it is being performed for, and how the information will be used. If the survey involves sensitive or identifying information, such as the respondent’s address or income, assurances should be given that this information will only be used for statistical analysis and will not be divulged outside the survey team. As interviewers gain experience, they can adjust their introduction to respond to varying situations and the mood of the respondents. However, field supervisors should make sure that the introductions retain the important points and do not become too casual.

Survey Design 61 Passengers arriving at the gate after the first boarding announcement who are reluctant to complete an interview survey could be provided a mail-back questionnaire, discussed below. While response rates are typically low, they do provide some responses from this passenger segment. The questionnaire should include a serial number, or other information identifying the day and flight number, and this information should be recorded so that the numbers of mail-back surveys handed out and returned can be tracked and appropriate weights can be assigned. Telephone Surveys Telephone surveys are in many ways more difficult than intercept interview surveys. Because neither the interviewer nor the respondent can see each other, it is more difficult for the inter- viewers to tell whether they have reached an appropriate respondent. Also many people are so tired of telephone solicitations masquerading as surveys that they are likely to be quite suspi- cious, if not hostile. Therefore the initial introductory script is all the more critical. It may be helpful to send an advance letter, when possible, explaining the purpose of the survey and indi- cating that a follow-up call will be made. Other fairly standard practices that can help improve response rates include stating the expected length of the survey, if this is fairly short, and identifying a specific time to call back if the current call is inconvenient or the desired respondent is not available. Mail-Back Surveys Mail-back surveys do not face the problem of contacting potential respondents as long as the mailing addresses are correct. However, response rates from mail-back surveys are gener- ally much lower than for telephone surveys, because there is no direct personal contact. The survey should be accompanied by a cover letter explaining the purpose of the survey, prefer- ably signed by an appropriate official of the sponsoring organization, such as the airport direc- tor. In the case of airport employee surveys, it may be preferable to have the cover letter issued on the letterhead of the employer and signed by an appropriate official, at least for large employers. A response date should be set to allow a reasonable time for completion of the survey and for follow-up reminders to be sent if a response is not received by that date. There is a rapidly dimin- ishing response rate to follow-up reminders, so it will generally not be worth sending more than two reminders. In cases where there is a relatively small target sample, such as airport employ- ees, it may be worth making follow-up telephone calls and performing the survey by telephone if the recipient is available, rather than sending follow-up letters. Mail-back surveys that are handed out to potential respondents, such as to air passengers in an airport departure lounge, do not generally permit any follow-up unless contact information has been obtained in the course of distributing the survey. In this case, response rates may be improved by offering some inducement to participate in the survey. One technique that might be considered is providing a pen with the survey form that is marked with the name of the sur- vey. This inducement will not only facilitate completion of the survey, but also serve as a reminder to do so. Asking potential respondents whether they would be willing to complete a mail-back survey before handing them the form may also help improve response rates by creat- ing an implied commitment on the part of the respondent. With all mail-back surveys, providing a pre-paid return envelope—or designing the form so that it folds to show the return address and pre-paid postage—is essential to increasing response rates. Consideration may need to be given to providing forms to be returned from international destinations, such as using International Business Reply Service envelopes. Although they are more expensive than regular mail, costs are incurred only for those returned.

62 Guidebook for Conducting Airport User Surveys Internet Surveys Respondents to Web-based surveys are generally contacted by email to request their partici- pation. Follow-up reminder emails can be sent at regular intervals to those who have not yet responded, although this produces the same diminishing returns as reminders to mail-back sur- veys. With a limited and well-defined target sample, it may be more effective to follow up by tele- phone, or even to call before sending the first request by email. Such a call will help ensure that the correct respondent has been identified and prepare the respondent for receiving the survey request. A telephone call will also avoid sending unnecessary reminders in cases where the respondent does not wish to participate in the survey. The survey software should give the respondent the opportunity to save partly completed responses and return to complete the survey later, particularly for longer or more complex surveys. 4.8.2 Refusals and Incomplete Surveys It will generally be useful during the course of a survey to record refusals and monitor incom- plete surveys. Monitoring incomplete surveys should distinguish between the following: • Those where the respondent terminated the survey before the end, possibly due to the need to board a flight or undertake some other activity, but the survey was complete up to that point. • Those where the survey was ostensibly completed but some questions that should have been answered were not. Comparison of refusal rates and incomplete surveys across interviewers may identify field staff who have a higher refusal or incomplete rate than average and could benefit from closer super- vision or additional training. Incomplete surveys may still provide useful information for those questions that were answered, and the data analysis phase of the survey should consider how best to make use of this information. For example, responses for completed questions in an incomplete survey can be included in frequency tabulations of those questions, although it will not be possible to include them in cross-tabulations with questions that were not answered. Where the contract for a sur- vey requires the contractor to meet a certain target number of completed surveys, a decision should be taken on which questions must be answered before a survey is considered complete. 4.8.3 Other Languages The two language issues to be considered regarding survey populations that do not speak English are the local languages of the area and the language of the target airport users to be interviewed. If the airport is serving a bilingual or even multilingual area, the interviewers will need to speak those languages, particularly if the area is officially bilingual.14 If the survey results are to be truly representative of the population, the multilingual nature of the area must be reflected in the sur- vey process. As well as multilingual interviewers, this process calls for multilingual questionnaires and other handouts. Translations must be of excellent quality to maintain the meaning of each question and response option. Where only a small proportion of the local population cannot communicate effectively in English, the need for multilingual interviewers becomes less clear. In the case of a flight-based sur- vey, at least one multilingual interviewer should be available, if possible, for each flight surveyed. 14 Note that a requirement for bilingual or multilingual interviewers will increase the wage rate.

Survey Design 63 The second language issue concerns international passengers. As the number of people flying internationally continues to grow, more and more languages are being spoken at airports, par- ticularly at major gateway international airports. This prevalence of multiple languages is a real problem for surveys and one for which there is no ready solution. The survey planning team must determine if this will be an issue and attempt to arrive at a workable solution. Where inter- national passengers are primarily from a small number of countries, bilingual or multilingual interviewers could be scheduled to survey the appropriate flights. It will not usually be feasible to translate questionnaires into many languages, but if most passengers who cannot speak English speak a common language, a translation in this language could be developed. If the survey team is conducting a strict sampling process, the language barrier may interfere with this process and lead to some bias in the results. A related issue is that travelers whose first language is not English may appear to understand the questions, but in fact do not fully under- stand them and give incorrect answers. It is important that interviewers be trained to identify such situations and that they devote time to ensuring that the respondents understand the ques- tions and they understand the responses. A benefit of using a multilingual questionnaire is that it will allow the survey team to exam- ine whether the characteristics of non-English-speaking respondents are significantly different from those of English-speaking respondents, and thus how important it is to make special arrangements to include these respondents in future surveys. 4.9 Use of Electronic Data Collection Devices There is a growing interest in using hand-held electronic data collection devices (EDCDs) for performing interview and observation surveys. These devices have a number of distinct advan- tages over printed forms, as discussed in the following subsection, but also raise several issues that need to be carefully considered. 4.9.1 Advantages and Disadvantages One of the most obvious advantages of using EDCDs is the elimination of the data entry task and the associated potential for errors to be introduced in the data. EDCDs store the recorded data directly in a database that can typically be downloaded and combined with the corresponding data from other devices. Questions are displayed and responses are entered using a program running on the device. While the capabilities of commercial software for data capture vary, most, if not all, programs provide the capability of exporting the data in a format that can be read by or imported into commercial statistical analysis software packages and spreadsheet software. This capability can represent a significant cost and time savings, as well as eliminate a potential source of error. Some survey sponsors have raised the concern that the absence of a paper form means that there is no opportunity to go back and check the validity of the data in the data file. This is true, but no different from the use of paper forms. There is no way with paper forms to check whether the response that was recorded on the form is in fact what the respondent said or intended. The use of paper forms does allow the data entry task to be checked for errors, but this is an irrele- vant consideration with EDCDs because the task is eliminated. The electronic data files should of course be backed up regularly so that they can be restored if they become corrupted. There is also the possibility that failure or loss of an EDCD could result in the loss of the data stored on the device. This possibility is no different from the possibility of loss or accidental destruction of paper forms before the data have been extracted from them. Modern EDCDs are quite robust and preserve their data if they lose power. Survey procedures should provide for

64 Guidebook for Conducting Airport User Surveys periodic downloading of the data on EDCDs. Some devices can do this while in use through a cell phone or Wi-Fi capability. In the final analysis, if a survey sponsor wants a paper backup to the electronic data file, one can always be printed out. One caveat is that with paper forms, well-trained interviewers sometimes make notes on the forms to clarify responses or suggest cautions in interpreting the response. Depending on the software, programming EDCDs to provide the same capability may be possible, but entering these comments typically takes longer on an EDCD than on a paper form. A difficulty with using EDCDs is that they cannot be used to survey passengers who are hur- rying to catch a flight, because (unlike printed forms) they cannot be handed out to respondents to take with them. Inability to survey such passengers can result in biased information if these passengers have different characteristics from those interviewed. This issue can be addressed by providing interviewers with mail-back forms to hand to passengers in this situation. Because the response rate from mail-back forms is typically quite low, the number of such forms handed out should be recorded on the EDCD (including the serial number of the form and where distrib- uted) so that appropriate weights will be assigned to those forms that are returned. Use of EDCDs introduces additional costs for purchasing or renting the devices and the soft- ware and programming the devices. There will also be logistical issues regarding availability and recharging of devices. The requirement to be able to use EDCDs efficiently can limit the appli- cants when selecting interviewer staff, to some extent, and can introduce the need for additional training. These issues are discussed in the following subsections. Survey Design and Data Quality An important advantage of EDCDs is that they allow more complex branching based on responses to prior questions and can tailor subsequent questions to information already pro- vided. While branching can also be done with paper forms, it can quickly become unwieldy and confusing if there are more than a few such branches. There is no such limitation with an EDCD program and the resulting logic is transparent to the user. Thus survey questions can be tailored to individual situations and the questionnaire can include questions that apply to only a few respondents without affecting the questions asked of others. The ability to tailor questions on the basis of prior answers can also shorten the length of time required to conduct the survey by skipping questions that are not applicable to particular respon- dents. Also, with paper forms the questionnaire may appear very long to the respondent and adversely affect the response rate, but the length of the survey is not evident to the respondent when using EDCDs. However, for this reason it is generally advisable to inform respondents of the likely time required to complete the survey. Another advantage is the ability to do real-time data checking and ask follow-up questions to clarify apparently inconsistent responses. This ability allows the interviewer to correct misunder- standings or mistakes while the respondent is still available. In other cases it may provide an expla- nation for what appears to be inconsistent information but is in fact an unusual or unanticipated combination of circumstances. This is a powerful feature. As more detailed information becomes available about air passenger travel patterns, for example, it has become clear that the range of traveler behavior is much wider than is commonly assumed. Therefore, trying to fit the full range of behavior into only a few simplistic categories can lead to a misunderstanding of the situation. Cost and Technical Support Considerations Although EDCDs provide powerful capabilities, the units themselves can be fairly expensive and a large number may be required for a given survey. Survey firms and airports conducting fre- quent surveys will generally acquire their own equipment and allocate the cost over many differ- ent surveys. It may be cost effective for infrequent survey sponsors to rent units. In this situation,

Survey Design 65 it would be desirable for the survey planning team to purchase a few units for questionnaire devel- opment and post-survey use, but rent additional units for the period of the survey. There is also the cost of the data entry software to be considered. Depending on the software used, license fees can cost as much as the units themselves. However, the cost of the equipment and software has to be balanced against the saving in data entry costs, both for the current survey and for future sur- veys that will use the equipment. While the technology involved in using EDCDs will be familiar to anyone with a personal dig- ital assistant (PDA), some technical support will be necessary, particularly for programming the units and downloading the data. Survey firms with experience using EDCDs should be able to provide this level of technical support, either with their own staff or though a subcontract with a technical specialist who has appropriate programming experience. 4.9.2 Choice of Equipment The choice of equipment for EDCDs involves tradeoffs between cost, capability, and ease of use. With increasing capabilities in terms of memory, screen size, and battery life, standard PDAs are becoming widely used for survey data collection. Custom devices that have been designed specifically for use in survey data collection are also available. These generally have larger screens and keyboards but are typically bulkier and heavier, and thus harder to use. The ability to hold the unit in one hand while entering data with the other is an attractive feature of PDAs. Consideration should also be given to the need for staff to hold the units for extended periods of time while standing; therefore, compactness and light weight are distinct advantages. On the other hand, a small screen limits the font size and the number of response options that can be displayed on one screen, while a compact keypad is more awkward to use and more likely to lead to mistyping. The principal factors to consider in selecting equipment are • Screen size and clarity. • Data storage capacity. • Software that can be used. • Use of keypad versus stylus. • Key size and keypad layout. • Battery charge life and recharge time. • Weight and handling. • Data export capability. • Wi-Fi or cell phone capability. • Cost. Laptop and tablet computers have been used for some survey applications where complex, graphically intensive screen displays need to be shown to respondents. However, these are awk- ward to hold for extended periods and would require either that respondents and interviewers be seated during the interview or that interviewers be provided with a mobile cart to support the unit. 4.9.3 Programming Considerations Selection of software to program EDCDs involves the choice between purchasing commercial software and developing a custom program using a suitable programming language. Commercial software is available that has been designed for programming surveys on EDCDs, particularly PDAs. The more advanced software generally includes the capability to present the usual types of questions and response formats, including categorical check-box questions and free text input, as well as to program skips to different questions based on the responses to prior questions. However, this software often has limited ability to display sophisticated graphics or custom screen layouts. Thus for applications that require this capability, it may be necessary to

66 Guidebook for Conducting Airport User Surveys develop a custom program. In this situation most survey sponsors will retain a survey firm that already has this capability. Selecting an appropriate commercial software package involves deciding which program fea- tures and capabilities are required and which packages support the EDCDs being considered. The choice of EDCD and software should be approached as an integrated decision, because such issues as screen size and keypad design interact with how the software displays the questions and allows the responses to be entered. As with any other software and hardware, capabilities are continually evolving and hardware costs are dropping, so the survey planning team or contractor will need to assess the currently available technology before making a purchase. Some questions to consider when reviewing commercial software follow: • What question formats are supported? • Can the software combine different types of question format (e.g., both check-box responses and free-text answers) in the same screen display? • How does the software handle questions that have more response options than will fit on a single screen? • What are the limits to the number of response options a given question can have? • Can the user customize the code that is used for each categorical response for a given question? • Can the user customize the order that categorical responses appear on the screen? • What are the limits to the number of questions? • Can the software use an existing data file to control what response options for a question are displayed based on prior responses (e.g., listing hotels in a given city)? • Can the software display response options based on the first few characters entered (e.g., sug- gesting city names based on the first two or three letters)? Do the options get refined as more letters are entered? • Can the user restrict the format used for numerical entries (e.g., require that a zip code have five digits and no decimal point)? • Can the user specify a template for numerical entries (e.g., telephone numbers as xxx-xxx-xxxx)? • Can the user specify range and consistency checks to be made on numerical responses? • Does the software provide specific capabilities to enter dates and times? • Does the software support touch-screen responses? • Can the software display a keyboard on screen for entering free text? • Can the software display graphical features? • Can the software allow the user to select a location on a graphical feature (e.g., a location on a map)? • Does the software allow logic branches, and how easy is it to program logic branches? • How much memory or disk space does the program occupy? • How much memory or disk space is required to store each survey response, and how does this vary with the number of questions? • What data download formats does the software support? 4.9.4 Survey Logistics Other considerations also need to be taken into account in using EDCDs. There will need to be a secure room where the equipment can be left when not in use and where the data can be down- loaded. It will usually be necessary to have spare batteries that can be charged while the units are in use or to have spare EDCDs to use while others are being recharged. Downloading the data from the units will typically require a desktop or laptop computer. Access to a telephone line or Wi-Fi link will allow the downloaded data to be transferred to a central database on a regular basis. Because the units themselves are fairly expensive (several hundred dollars each), appropriate steps

should be taken to ensure their security while in use. Units should be checked in and out to sur- vey staff at the start and end of each shift, and staff should be trained not to let them out of their possession while they are in use. It may be prudent to provide each unit with a short tether that can be clipped to the interviewer’s apron or vest to help prevent loss and damage. 4.9.5 Staffing Considerations Use of EDCDs will generally require staff training. Some older interviewers may have less experience handling small electronic devices, may have difficulty using the small keypads or see- ing the screen display fonts, and may require additional practice to become comfortable using the devices. The other staffing consideration relates to programming and technical support. The program- ming can be subcontracted if nobody on the survey planning team has the necessary skill and expe- rience, but this will incur additional cost and administrative effort. The team will need to coordi- nate closely with the programmer to ensure that the finished program performs satisfactorily. Although technical support in the field does not require the same level of specialized skill as pro- gramming, and will generally be within the capabilities of survey supervisory staff, some training may be required beforehand if the field supervisors have not performed this function previously. 4.9.6 Summary Although EDCDs offer a number of distinct advantages, experience in their use for airport user surveys has been mixed. Problems can arise if their use has not been carefully planned and thought through. As with any evolving technology, some of the difficulties that arose with the early hardware and software have been overcome. Even so, the effective use of EDCDs requires some technical skills and experience. Survey sponsors should consider on a case-by-case basis whether the advantages justify the effort involved. In general, hand-held EDCDs are only prac- tical to use with interview surveys. Printed forms will typically be required for self-completed surveys. Surveys with the following characteristics tend to favor the use of EDCDs: • A long or complex set of questions with multiple branches. • The need to tailor questions to the respondent’s answers to earlier questions. • Questions with a large number of categorical response options. • A large sample size (resulting in high data entry costs). • The desire to include data consistency checks during the survey interviews. • Availability of survey staff with experience in the use of EDCDs. • The survey is likely to be repeated frequently (spreading the cost of programming over several surveys). On the other hand, surveys with the following characteristics may be more appropriately per- formed using printed forms: • A fairly simple questionnaire with limited branching. • A relatively small sample size. • Straightforward questions that do not require data consistency checks. • Respondents with limited time to answer questions, who may need to be given the survey form to complete and mail back later. • Respondents need to enter information or complete the questionnaire themselves. • Lack of staff with appropriate experience in the use of EDCDs. • No plans to repeat the survey in the near future. Survey Design 67

4.10 Data Entry and Quality Control 4.10.1 Data Coding, Data Entry, Verification, and Editing Data coding refers to the assignment of numeric codes to the various response options. Typically, this is done at the time the questionnaire is developed and the codes are shown on the printed survey form to assist in data entry or embedded in the EDCD program. In some cases, responses in free-text fields are assigned numeric codes in a separate field, particularly where the same response recurs frequently in the data, such as hotel names. Although response codes can be omitted from printed survey forms and provided to the data entry staff as a separate docu- ment, this procedure may require them to refer to two different documents during data entry (depending on the data entry software) and may slow down the data entry and/or introduce data entry errors. It will of course be necessary to define any response codes for commonly occurring free-text responses after the survey has been performed. Data entry involves transferring the survey response data from the survey forms to a computer file using the numeric codes shown on the survey form or developed later and defined in a sur- vey codebook. Two methods may be considered: • Manual data entry, using survey staff (or others) retained after the survey data collection for this purpose. This method is labor intensive and subject to data entry errors. • Mass-scanning techniques, using high-speed scanning hardware and software that is capable of automatically coding responses into a database. Further information on this method, including pros and cons, is provided in Appendix E. There are two aspects to data verification: • Checking that the data entry was done correctly. Ideally this involves repeating the data entry task with different staff and comparing the two files. Data entry software typically provides a verification function that compares the second data entry to the original file and flags any dif- ferences. Any discrepancies are then resolved with reference to the survey forms. However, this technique doubles the data entry cost. A less expensive but less reliable approach involves verifying a random sample of survey forms. This technique will establish whether the required accuracy for data entry has been achieved, but of course cannot identify and correct any errors on the survey forms that are not included in the verification. • Analyzing the data to identify any obvious errors, inconsistencies, or apparently illogical responses. This can address such issues as whether a trip origin zip (postal) code is in the reported city, and whether the street name of a reported address exists in the city indicated. A common problem is misspelling of free-text data, such as city or street names, or switching digits in zip and postal codes. Checks can be run to make sure that respondents reporting the use of ground transportation services reported trip origins in locations where use of the ser- vice would be plausible. Numerical responses can be checked to ensure that they are within a reasonable range. Free-text responses in the “Other” category of categorical questions should be reviewed to determine whether the response should have been given as one of the defined categories. In some cases, an error will be fairly clear, such as misspelled names or transposed digits in a zip or postal code. In other cases, it may be less obvious what the correct answer should have been, or even whether there is an error at all. Data verification can be very time-consuming if done thoroughly, but the overall quality of the survey data is greatly improved by devoting adequate resources to this task. The majority of the required effort lies not so much in identifying apparent errors in the data, which is fairly straightforward, but in the research necessary to determine what the correct response should have been. For example, it may be fairly easy to determine that a zip code is not in the reported city, but figuring out what the error is in the zip code, or even whether the zip code is correct but 68 Guidebook for Conducting Airport User Surveys

Survey Design 69 the city name wrong, is much more time-consuming. The more redundant information that is obtained in the survey, such as asking for both the zip code and state (or province) of a respondent’s home, the easier it is to identify and correct any errors. “Self-completed Surveys” in Section 5.2.2 includes a discussion on the verification of air party size that may be helpful in understanding what can be involved in the data verification and cleaning process. Data editing is the final step in the process and involves making the necessary changes to the data file to correct any known errors. It is good practice to preserve the originally reported data in one set of data file variables (these may be referred to as fields or columns) and copy the data to a different set of variables before editing it. This procedure allows the data that have been changed to be identified later. Then changes can be revised—or even reversed—if subsequent information comes to light. 4.10.2 Benefits of Using Interviewers for Data Entry Where the survey takes place over a relatively long period, such as several weeks, it is highly desirable to start on the data entry and verification process while the survey is still in progress. This can help identify any problems with the survey questions or procedures while there is still some opportunity to correct them during the remainder of the survey. When the survey schedule permits, it may be advantageous to have contract staff hired as interviewers spend some time assisting with the data entry task. Exposing them to the difficul- ties involved in transcribing the information from the survey forms might lead them to take more care with the way they record responses during the remainder of the survey. Also, because extra interviewers are usually required as backup, using them for data entry helps keep them pro- ductively employed when they are not required for interviewing. In general, however, temporary staff hired as interviewers will not have the data entry skills to efficiently perform the majority of this work. In addition, they will generally not have enough local knowledge about the airport and ground transportation system to perform effective veri- fication and error correction. Therefore verification and error correction will require the active involvement of the survey planning team and possibly the assistance of other operations or plan- ning staff with the necessary local knowledge. 4.11 Analysis and Reporting of Survey Results At this stage of the project the survey data collection is complete, the data have been entered into appropriate databases, and the data have been checked for the internal integrity of each response and cleaned accordingly. It is now time to undertake the analysis, as determined by the goals of the survey project. 4.11.1 Considerations for Doing the Analysis In-House When the analysis will be completed by in-house staff, the resources necessary may not need to be included as part of the survey project budget. It is appropriate to use in-house resources if the following considerations make it feasible: • There is sufficient expertise in-house to complete the tasks listed in this section, and this expertise is available in a timely fashion after the data collection period. • The appropriate software and hardware exists to complete the analysis. Modern spreadsheet applications have many data analysis capabilities. The requirements may extend beyond these capabilities, in which case the survey sponsor should consider using the more powerful statis- tical features of applications such as SAS® or SPSS®.

70 Guidebook for Conducting Airport User Surveys 4.11.2 Weighting and Expansion Once the data have been cleaned and made available to the analyst, one of the first priorities is the assignment of one or more weighting factors to each interview response. In the case of sam- ple surveys that have been conducted according to a strict sampling plan, the response weights will be determined as part of this plan, as discussed in Sections 3.5 and 5.5. These weights can be added to each interview record. In the case of groundside surveys, discussed in Section 5.9, there will be one weight assigned to the interview record based on the vehicle count at the facility and a second weight assigned based on the passenger volumes. The analysis may utilize either of these weight factors depend- ing on the focus of the results, passenger versus vehicle. Depending on the available data, these census counts might include the following: • Air passenger counts, possibly by hour or by day. • Parking ticket counts. • Automated vehicle identification system counts for modes other than private vehicles. • Roadway traffic counts. • Control count observation surveys—such as at the curb area, security clearance area, or other suitable location—for determining the effective sampling rate and weighting of responses to be used in the analysis. 4.11.3 Tabulation and Interpretation Tabulation and interpretation are the core of the analytical process. Typically, this process begins with basic frequency counts of the key variables and cross-tabulations. This step can often reveal unexpected relationships as well as unexpected problems in the data. It is recommended to do basic frequency counts on all variables to get an initial look at the numbers of valid responses for each question. The process of data analysis is determined by the goals of the survey and is often a personally defined process, unique to the analyst. Invariably the analysis will reveal many interesting results that appear to warrant further analytical effort. However, further analysis should only be pur- sued as time and resources permit. It is in these secondary analyses that the additional value of the data will be exploited. 4.11.4 Survey Accuracy and Limitations An important, but sometimes overlooked, purpose of the data analyst is to identify the accu- racy of the results as well as the limitations within the survey data. Where results are provided for subgroups of the population, the accuracy of the estimates for these subgroups should also be identified. In some cases • The sample size may not be sufficient, and consequently it may not be feasible to drill down to increasing levels of detail. • The conduct of the survey or response rates will produce limitations in how the data can be analyzed or the level of detail that can be achieved in the analysis. Avoiding these limitations is a key reason to include the expertise of a data analyst from the outset of the survey project. • The limitations may be a function of the questions, how they are coded, and what responses were obtained. These limitations may not be revealed using data analysis techniques alone. 4.11.5 Report Preparation and Presentations The primary reports and presentations must be directed towards the goals and purpose of the survey. A formal report is generally required and will be a substantive document that fulfills the

requirements of the survey project. A presentation on the results of the survey, which addresses the purpose of the survey and explains what was obtained for the funds approved, will close the loop with senior management. 4.11.6 Publications The entire survey project, while unique to the agency and airport involved, may include aspects that are of potential use to a wider audience. In this regard, consideration should be given to publicizing the survey results to parties beyond the original survey planning team. The deci- sion to publicize the results is the responsibility of the survey sponsor. There are many forums where such publications would be welcome. Because there are many airports conducting surveys at any time across the country and around the world, other plan- ners may just be beginning the process and would benefit from the knowledge gained from this survey. Perhaps the single most effective way to distribute information about airport user sur- veys is for survey sponsors to post the survey reports on their websites. 4.12 Post-Survey Analysis: Lessons Learned The periods immediately following the survey and after the analysis are important times to sit back and reflect on the survey. Chances are that there are a number of things that went really well. It is also likely that some things did not go as well as planned. Documenting this informa- tion at this point will prove worthwhile when it is time to do another survey in the future. For both the things that went right and the things that went wrong, it is important to docu- ment why this is the case, and what the thinking was underlying the various decisions. Especially important is documenting what went wrong, why it went wrong, and how it should be done if it had to be done again. At this closing stage of the project there are probably some ideas and thoughts that can be included in this document that will help in the future. During the survey, the project team probably received many comments—from supervisors, interviewers, and even the airport users who were interviewed—about things that could have been done better. Documenting all these comments will ensure they are considered before the next survey, when improvements can be made at the design stage. 4.13 Documenting the Survey It is important to record as much as possible about the survey. The importance of recording what went right and what went wrong has already been emphasized. Throughout the survey project, a number of other documents will have been created for various purposes. All this doc- umentation should be preserved for possible re-use in later surveys. Documents that are likely to have been created and that should be maintained for future use include the following: • Survey design reports (including sampling procedure, survey plan, logistics documentation, etc.). • Requests for Proposals for any contractors. • Training materials. • Survey questionnaire. • Data entry or transfer software. • Survey analysis reports and presentations. Survey Design 71

72 Guidebook for Conducting Airport User Surveys • Lessons learned. • The data. Of all the components of the survey, the data are the most valuable. This information, after all, is what the money was spent to collect. Even after the analysis is completed, these data will be invaluable in the future. 4.14 Summary This chapter has covered the general aspects of planning an airport user survey and outlined issues common to all surveys. Planning tasks specific to the particular type of survey to be con- ducted are described in the following chapters. It is clear that planning an effective airport user survey requires careful consideration of a large number of different factors. It follows that adequate resources and time need to be allocated to the planning stage. The appropriate level of resources and lead time will vary with the circum- stances of each survey—in particular, whether the survey is being performed for the first time or is repeating a former survey. For an air passenger survey with several thousand respondents being performed for the first time, the planning stage could require as much as 20% of the overall budget and should commence at least six months before the planned data collection. The time required is considerable, but the quality of the resulting information will depend on the effort devoted to sound planning.

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TRB’s Airport Cooperative Research Program (ACRP) Report 26: Guidebook for Conducting Airport User Surveys explores the basic concepts of survey sampling and the steps involved in planning and implementing a survey. The guidebook also examines the different types of airport user surveys, and includes guidance on how to design a survey and analyze its results.

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