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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.

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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.

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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.