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8 Guidebook for Conducting Airport User Surveys Airports function within the air transportation system and indeed within the larger transporta- tion system therefore, airport managers and planners must understand the nature of the market being served. This includes such issues as the trip purposes and travel patterns of passengers using the airport, as well as the nature of goods being shipped through the airport. Where the local travel market is served by more than one airport, it is helpful to understand relative market share and the factors that influence this. Depending on the length of the trip, travelers and shippers may also have a choice between air and surface transportation (i.e., car, bus, truck, rail, or sea). Effective planning and management of airport facilities and services also require an understand- ing of the characteristics, needs, and satisfaction of the customers using the airport, principally the air passengers and shippers but also the intermediate service providers, such as the airlines, freight forwarders, and ground transportation providers. This customer information might include air travel party sizes and the amount of baggage checked by air passengers, as well as customer satis- faction with the services provided by the airport and suggestions for how they can be improved. While some of the information needed for effective planning and management of airports can be obtained by direct observation or from statistics that are routinely collected, much cannot. Some airport user attributes are not directly observable and some statistics are not routinely collected. Airport user surveys are the only way to obtain information of this type, including the following: Air passenger characteristics for facility planning, such as arrival time before flight departure or the number of well-wishers accompanying passengers into the terminal. Customer satisfaction with airport facilities and services. Air passenger and airport employee satisfaction with existing concession services and likely use of additional services. Ground transportation used by air passengers and airport employees to travel to and from the airport, particularly public transport. Trip origins and destinations of airport users within the region served by the airport. Use of competing airports and the factors affecting the choice of airport. Economic impact of the airport on the surrounding region. Having good information on the wide range of issues typically addressed by airport user sur- veys improves the quality of planning and decision making. At the same time, obtaining good information costs money. In deciding how much effort to devote to collecting this information, consider how the information will be used and the likely costs of poor planning, design or oper- ating decisions. In general, where information will be used in planning new facilities, the cost of a survey will be small compared to the cost of the facilities. The ability to appropriately size the facilities and phase future expansion could significantly reduce the cost of a project or forestall the need for expensive modifications after construction has commenced or the facilities have been opened. In planning an airport user survey, or even deciding whether one is necessary, airport planners and managers need to consider what information is already available, what additional informa- tion is needed and how accurate that information needs to be, and then balance the cost of the survey against the value of the resulting information. This is not an easy task. One goal of this guidebook is to help airport planners and managers address this issue. 1.3 Survey Concepts For readers who are considering performing a survey for the first time or have limited expe- rience with surveys, this section provides an overview of the basic concepts and some of the common terminology used in survey practice.

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Introduction 9 The purpose of an airport user survey is to gather information about the characteristics or opinions of a defined group of airport users, such as air passengers using the airport or those employed at the airport. This group is referred to as the target population to be surveyed (often shortened to population). In general, it is not practical to gather the desired information from every member of the target population, so a subgroup of the target population is selected. This subgroup is referred to as the sample. The process of performing a survey involves selecting an appropriate sample, requesting the desired information from each member of the sample, ana- lyzing the responses and reporting the resulting findings. The process of performing a survey starts by planning each of these steps. When planning a survey, consideration needs to be given to clearly defining the target popu- lation, as well as deciding how large a sample is required and how to select the sample of respon- dents. These are not always obvious decisions. For example, in performing an air passenger survey, is the target population all passengers using the airport in a given period, including those con- necting between flights, or only those starting their air trip at this airport? Is the target population only departing passengers, or does it include arriving passengers as well? The answers to these ques- tions will affect the survey methodology as well as the approach to selecting the sample. Guidance on addressing these issues is provided in Chapter 4, "Survey Design." Ideally, a survey sample would be randomly selected individuals from the target population, where random selection means that any individual in the target population has an equal likeli- hood of being selected. This random selection is necessary to be able to make inferences from the sample about the characteristics of the target population with known statistical confidence. However, in practice such random selection is often difficult to achieve. The methods used to select survey respondents inevitably constrain the selection so that it is rarely completely random. For example, if an air passenger survey of selected flights is conducted in airline gate lounges, the sample is necessarily restricted to those passengers in the lounges in question, who are generally passengers on the flight about to depart from that gate. The respondents on any given flight will generally have a different distribution of characteristics from the target population as a result of the specific market served by the flight, the time at which the flight departs, and possibly other factors, such as the airline in question. Even if the flights to be surveyed have been randomly selected, it is unlikely that the selected flights will cover all possible combinations of market, airline, time of day, and day of week, because of budgetary limitations on the number of flights that can be included in the survey. The smaller the number of flights sampled, the less likely it is that the characteristics of the passengers on those flights will correspond exactly to those of the target population as a whole. A sample in which the distribution of characteristics in the sample differs from the population is referred to as a biased sample. An important aspect of planning a survey is designing a sampling strategy to reduce potential bias and applying techniques to control for any bias that remains. These techniques involve assigning weights to each response, so that the weighted results more closely cor- respond to the expected distribution of the characteristics of the target population. Of course, this implies some knowledge of that expected distribution and a method to calculate the response weights. These issues are discussed in more detail later in this guidebook, in the chapters specific to each type of survey. Having selected the sample, the survey respondents are then asked to provide the desired information through the use of a survey instrument or questionnaire1. The design of the survey 1 Survey instrument is broader than questionnaire as it includes, for example, data recording sheets in observational surveys. The airport user surveys discussed in this guidebook exclude observational surveys and the term questionnaire is used through- out this guidebook.