Self-completion questionnaire surveys are one of the most widely used forms of survey technique in transport. Self-completion surveys are defined to be those which the respondent completes without the assistance of an interviewer. With this type of survey, respondents are required to perform the three tasks on their own. These three tasks are to read and understand the question, to mentally formulate an answer, and to transcribe this answer onto the questionnaire form itself. In personal interview surveys, the respondent is wholly responsible only for the second of these three tasks; the interviewer is primarily responsible for the first and third.
Several types of basic survey format can be described, depending on the methods used for collection and distribution of the questionnaire forms. These variations include:
(a) Mail-out/mail-back surveys
This is the most basic form of the self-completion survey and the one that is most often employed. The questionnaire is mailed to the respondents and they are asked to return it by mail after they have answered the questions. The return postage is generally paid by the survey designer, although the precise method by which this postage is paid can have an effect on response rate as will be described in Chapter 7.
(b) Delivered to respondent/mailed-back
Where it is suspected that response rates may be particularly low, or where it is believed that respondents may need some personal instructions on how to complete the survey form, it may be desirable to personally deliver the questionnaire form to the respondent. In this way the purpose of the survey can be explained, any questions about the survey can be answered immediately, instructions can be given, and questions answered, about how to fill out the survey form. Such personal contact will generally increase the response and will also result in a higher quality of response to the questions.
(c) Delivered to respondent/collected from respondent
In addition to delivering the questionnaire form, it is also possible to collect the form from the respondent at some later date. This further increases the response rate by putting some pressure on the respondent to complete the survey before the collector returns, and also enables the collector to resolve any specific problems which the respondent encountered while filling out the questionnaire form. Naturally, however, the increased response obtained in methods (b) and (c) can only be obtained at considerable extra expense for the personal delivery and collection of the questionnaire forms. However, where a high response rate is essential, as in a National Census, then this method may be the most cost-effective way of obtaining these responses. This method is frequently used when "long-term" diaries (e.g. 7 day diaries) are distributed (e.g in the National Travel Survey in the U.K. (UK Department of Transport, 1993b).
Self-completion surveys have both advantages and disadvantages. The primary advantages of a self-completion survey include:
(a) Self-completion surveys are generally much less expensive than a comparable personal interview survey. Hitlin et al. (1987) estimate that the cost of a telephone interview survey was approximately three and one half times more expensive per completed response than a hand delivered and collected self-completion survey. A personal interview survey is even more expensive than a telephone interview survey (Ampt, 1989). Care needs to be taken, however, that this cost reduction is not a false economy. Self-completion surveys almost always have lower response rates than personal interview surveys, and hence the cost per returned questionnaire is much higher than the cost per distributed questionnaire. More important, the value of a returned questionnaire is a function of the overall response rate because of the effect of non-response bias. Thus, the value-for-money from self-completion surveys may be lower than it initially appears unless care is taken to minimise, or otherwise account for, non-response effects.
(b) A wide geographic coverage is possible in the sample, because postal charges do not generally vary as a function of the distance involved. It is usually just as expensive to send a questionnaire 1 kilometre in the mail as it is to send it 1000 kilometres. There is therefore no incentive to limit the sample to a local area (as there would be in a personal interview survey). The only restriction which needs to be considered is the time required for the mail to reach the more remote areas of the study area; this may be a critical factor in the design of a schedule of reminder letters.
(c) Because there is no interviewer involved in the survey, interviewer effects are eliminated as a possible source of response bias. The type of interviewer effects which can occur will be discussed in Section 3.2.6. (d) The respondent has ample time to consider the questions before
providing an answer, and hence it is possible to obtain considered responses to questions in a self-completion survey. It is also possible for a respondent to consult documents, if necessary, in order to provide factual information as an answer to a question (e.g. consult a log book to provide information about vehicle operating costs).
(e) The respondent can choose the time and place in which to complete the questionnaire (except for questionnaires which must be completed quickly, such as on-board a vehicle). Because of this, there is less incentive for respondents to hurry through the questionnaire in order to resume the activity they were engaged in when they received the questionnaire. This generally results in a more complete answering of the questions. The danger with allowing the respondents to defer answering the questionnaire is that they will completely forget about answering it. While the above advantages are attractive features of a self-completion survey in some circumstances, the self-completion questionnaire survey is not without some considerable difficulties, such as:
(a) The most consistent criticism of self-completion surveys has been the high level of non-response. Reported response rates of between twenty and fifty percent are not uncommon, and this allows ample opportunity for serious biases (see Chapter 9) to enter the data (Brög and Meyburg, 1981). However, by incorporating rigorous design and validation measures, more recent self-completion travel surveys in Australia have achieved response rates of up to 75% (Richardson and Ampt, 1993a). The most reliable way to address the response rate is to incorporate a series of reminder letters and/or questionnaires into the survey design - a methodology which raises the cost of the survey method to some extent. (b) The layout and wording of the questionnaire MUST be extremely clear
and simple. Definitions must be clear and easily understood by the population being studied (not just to the survey designer), because there is no interviewer on hand to clarify the intent of the questions. The amount of time and effort which must be put into questionnaire design is therefore considerable.
(c) With a self-completion survey, it is difficult to ensure that the correct person fills out the questionnaire form. Even though the questionnaire
may state quite specifically who should fill out the form, there is no guarantee that this occurs and there is no simple way of checking whether this is the case. In travel surveys, it is important that each person relates their own experiences to avoid the problems of under-reporting associated with proxy data (Ampt, 1981). It is therefore vital to incorporate validation measures which give some information on proxy reporting in the self-completion survey design.
(d) Responses from self-completion surveys tend to be skewed towards the more literate sectors of the population which tends to travel in a different way than the remainder of people. This means that rigorous follow-up procedures for non-respondents are required to ensure robust data.
(e) In general, only simple, one stage questions can be asked, since questions which require complex filtering, which depends on answers given previously, usually need the skill of an interviewer.
(f) In self-completion surveys the answers on the questionnaire form must be accepted as final; there is often no chance to probe further to clarify ambiguous or unclear answers. For this reason it is important to plan and test the inclusion of ways of following-up respondents. One way to do this is to ask for their phone number and phone if clarification is needed, and another is to follow-up a sample of people with a personal interview (Section 7.2.2).
(g) Spontaneous answers cannot be obtained in a self-completion survey, so opinions given may not in fact be the respondent's own opinion at that time, but may be the result of discussion with others at a later time. For this reason, self-completion surveys are generally not the best instruments for conducting attitudinal surveys.
(h) A self-completion questionnaire offers no opportunity for the collection of supplementary information on such things as the respondent's residential environment or the respondent's attitude towards the survey.
(i) Answers to questions cannot be treated as independent since the respondent has the opportunity to scan the entire list of questions before answering any of them. For this reason, obvious cross-checks which are transparent to the respondent cannot be used very effectively.
In summary, self-completion questionnaires are characterised by the ease with which they can cover a wide geographical area, and by their moderate cost. They need to have substantial effort invested in their physical design and appearance. Finally, the desirability of using reminder letters or questionnaires means that the
entire survey period needs to be considerably longer than that for personal interviews.