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29 This is not an easy balance to strike, because a successful survey, either alone or in conjunction with other survey geocode may be imperative to construct a stated-preference methods, has been made. experiment for the respondent later in the survey. Therefore, the survey must collect geographical data or it loses signifi- cant value for the researcher. One technique to resolve the Recruiting and Sampling Techniques for Transit Web-Based Surveys geocoding issue is to ask the respondent twice for their address to ensure it is typed correctly. If the database still fails There are a variety of ways to obtain web-based survey to find it, the respondent may then be automatically taken to respondents once the sample population is understood and a map screen and asked to indicate their address using the map considerations regarding coverage error have been addressed. tool that cannot fail as the result of an incomplete database. The study objective is also critical in deciding not only who, This technique has been employed in a number of transporta- but how, to sample. The following section describes two tion web-based surveys, including a significant transit study different types of studies; one for a wide geographical cover- currently underway evaluating a new transit service between age and the other for a more targeted sample. Lower Manhattan and JFK Airport. The following list presents some key considerations for Wide Coverage Study web-based researchers to use when designing the validation rules in their surveys (10): Sometimes it is necessary for the transit researcher to understand how their entire geographic region feels about a · Type of edits (e.g., format, conditional, and consistency transit-related research topic. This includes both riders and edits), non-riders for all demographics across the entire transit · Number of edits (i.e., determination of priorities), area. For example, if the transit researcher is concerned · Optimal timing of edits (after each question or just with who uses transit and why, it may be necessary to before the questionnaire is completed) with respect to randomly select households throughout the region using recall versus burden, random digit dial or address-based sampling for a mail-out. · Presentation of edit failures to respondents, Although there are a number of concerns about nonre- · Wording of error message (particularly ones calculated sponse error with random digit dialing and with mail sur- by the system), veys (1), these are still two of the most effective techniques · Design and format of the message (e.g., color and to randomly sample the population of a large geographic background), area. One of the limitations of web surveys is that there is · Use of hard edits (forced to fix in expected manner) currently no way to generate a random list of e-mails for or soft edits (either reconcile the error or provide potential survey respondents in a particular geographic comments), region. This limitation makes contacting random samples · Design and management of previous or complementary of wide areas difficult for web surveys. external information, and · Help facilities provided (e.g., additional instructions, Nevertheless, random digit dial could still be the recruit- telephone support, and e-mail responses). ment method: the transit researcher can contact potential respondents in the study area by phone, obtain their e-mail Although there are issues with item nonresponse error in address, and send respondents an e-mail invitation with a link web-based surveys, real-time validation and editing remain to the survey. The researcher can also give the respondent the as major benefits of conducting web-based surveys. The option of taking the survey over the phone at that moment. details of how, when, and whether to validate are important Completing the survey at that moment over the phone may and must be considered by all web researchers (transit or be convenient for the respondent, thus increasing the overall otherwise). response rate for the study; however, phone completions may reduce the number of respondents taking the survey by means of the web. Offering a web completion option can also SUCCESSFUL PRACTICES AND CHALLENGES help increase response rates to CATI surveys: an interviewer IN CONDUCTING WEB-BASED TRANSIT SURVEYS can send an e-mail invitation with a survey link to respon- dents who are resistant to completing the survey on the tele- The previous sections are intended to provide the phone. This method has been used with limited success in at researcher with an understanding of the strengths and limi- least one recent study. tations of different survey methods compared with web- based surveys and of the various issues to consider when As part of a paper-based, mail-out/mail-back survey, a choosing which survey method(s) to use to best serve their researcher can print a web address and unique password on study. This section discusses how to proceed in conducting each survey, providing the respondent with the option to take a web-based survey once the decision to conduct such a the survey by means of the web.
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30 Although both mail and telephone survey methods are the Customer Database most effective methods to ensure a random selection of respondents in a wide geographical area, both require the What is ideal is that once an e-mail address is obtained from relatively expensive methods of contacting respondents by the sample population, compiling a customer/potential cus- phone or mail. Once a respondent agrees to cooperate over the tomer database with e-mails is a powerful incentive to con- phone with a CATI operator, there is often little cost savings ducting research with riders and non-riders alike. Creating to having them take the survey on the web because, whereas a this type of database is a particularly important tool for rider web response is less expensive than a CATI operator research, because many riders use the transit system over a conducting the interview, there is no guarantee that the respon- span of years, and obtaining their e-mail address allows them dent will actually follow up and take the survey online. Fur- to be easily contacted later for any research the transit agency thermore, the greatest cost of a CATI survey is reaching a might require. For example, 65% of NJ TRANSIT commuter respondent and gaining their cooperation. Because this has rail riders have been riding the system for two or more years occurred, it is logical to see the survey through to its conclu- (2). Surveying this group, which has a large rider database, sion. Offering a respondent a web survey option on a mail-out becomes a matter of creating the sample objective and send- survey might increase response rates by giving respondents a ing out a batch of e-mails inviting respondents to participate. more convenient method to take the survey; however, those Although there is some additional fieldwork involved, respondents may have completed the questionnaire anyway because an existing database should be regularly updated to using the mail-back method. Therefore, it can be said that ensure new riders are being included and that the list stays respondents themselves may gain some benefit by using their current with changing demographics, conducting fieldwork preferred survey method; however, the actual response rate to update and maintain a rider database is a much less oner- may or may not increase; in the meantime, the costs related to ous task than having to obtain a large sample for every study. creating and administering the additional web-based survey To obtain such a database, a transit researcher starting from instrument have still been incurred (1). scratch with no customer list can send staff into the field and collect a very large sample of customer e-mail addresses. This can be done by asking for customers' e-mail addresses Targeted Sampling for Riders using interviewers or a simple, onboard, paper-based card questionnaire (see Figure 18). A broad geographic sampling frame may not be necessary for many studies that a transit agency might be conducting. The presence of an e-mail address is a strong indication of When this is the case, web-based sampling often becomes a web penetration within the transit area. Once the researcher strong survey option. has a list of rider e-mail addresses, web-based studies can be readily conducted. As the list matures, it will need to be reg- ularly updated owing to respondents who opt out or indicate Riders that they have stopped riding the transit service and to add Most transit studies do not require a random sample of a new riders into the customer database. Finding new cus- large geographic population. For example, when transit tomers and other customers not on the list can be done with agencies need to sample their ridership, they know how to the same card and intercept methods as used to compile the original list, but targeted on specific types of riders needed to find them: they are on board the vehicles, at the stations and complete the sampling frame for the customer database (see terminals, and possibly in their customer database. There- chapter six for examples of two projects that collected cus- fore, researchers conducting rider origindestination and tomer lists using web surveys). customer satisfaction surveys, for example, will be able to directly intercept riders using a paper-based, hand-out sur- vey or a personal interview on board transit vehicles or at Non-Rider Targeted Sampling transit stations and facilities. With a hand-out or interview survey, it is usually very easy to ask for an e-mail address Many surveys are project-specific, whereby certain targeted on the handout instrument or, in the case of the interview, to populations are needed to evaluate new service initiatives. directly ask for an e-mail address. Although onboard paper For example, if a new light rail system is proposed, a mode surveys are effective because the rider is "captive" during choice study will be necessary to understand the ridership their transit trip and has the time to fill out a survey, offer- potential for such a system. For studies such as this, ran- ing a web-based option or web-only survey can allow the domly intercepting respondents in the area of the proposed transit researcher to conduct much more complicated new service is an excellent way to sample. These respondents surveys and to develop a customer database for future can either take the survey on the spot or later using the web research needs as discussed later. That the rider will need to (after providing an e-mail address to the researcher). access the survey over the web later (and not right there on the transit vehicle) is not ideal, but as noted earlier, a self- When the targeted study population of a survey is non-riders administered web survey provides the ability for respon- of transit, web-based surveys can be very useful. Often one of dents to log in when it is convenient for them. the most important things for transit agencies to understand is