Household Personal Interview Surveys

A personal interview survey is defined as one in which an interviewer is present to record the responses provided by the respondent in answer to a series of questions posed by the interviewer. For this reason, many of the intercept surveys discussed in Section 3.2.5 as well as the telephone surveys outlined in Section 3.2.4 could also readily fall under this category. Our discussion in this section is, however, limited to personal interviews which take place in the home. Personal interview surveys have long been associated with transport, with home interview surveys providing the major means of data collection for the transport studies of the 1960s, 70s and 80s.

A household personal interview survey may be chosen, in preference to a self- completion survey, for any of several reasons:

(a) In general, higher response rates may be obtained from personal interview surveys than from self-completion surveys. Response rates of the order of 75% to 85% are not uncommon. This tends to minimise the effects of non- response bias, although it does not completely eliminate this bias as will be discussed in Chapter 9.

(b) The personal interview survey allows for considerable flexibility in the type of information collected. Attitudes, opinions, open-ended verbal answers and other non-quantitative information are much more readily collected in a personal interview survey than in a questionnaire survey. Complex sequence guides or filters can be used if required, since interviewers (unlike respondents) are always given training prior to the commence- ment of the survey.

(c) The presence of an interviewer means that explanations can be given regarding the meaning of questions or the method in which answers are to be given. As will be explained later (Chapter 7.3.2), the interviewer must generally adhere to a fixed set of questions, some of which need to be asked verbatim, but explanations of the meaning of questions are generally permitted so long as they do not influence the answer by the respondent. In a travel survey, this is particularly important in relaying information to respondents about the level of detail required for reporting trip and activity behaviour.

(d) Personal interview travel surveys can be carried out over a much shorter

time period than self-completion surveys which need up to 6 weeks

elapsed time to incorporate sufficient reminder notices into the survey procedure (see Section 7.2.1).

(e) Since many surveys can be quite long, an interviewer can be effective in

maintaining respondent interest and in ensuring that the full set of

questions is completed.

(f) By noting the interest of the respondent in the survey and the way in which the questions (especially attitudinal questions) are completed, the interviewer can make a valuable assessment of the validity of the recorded answers.

(g) The interview situation is valuable where it is desired to obtain

spontaneous answers from a particular individual. Thus interview surveys

are particularly suited, perhaps even essential, for attitude surveys.

While being particularly effective in several aspects of transport data collection, personal interview surveys are not without their own distinct disadvantages, including:

(a) Personal interview surveys are relatively expensive. Typically they would be three to ten times more expensive per returned questionnaire than a self-completion survey (this of course depends on the quality of the self- completion survey). The high cost of personal interview surveys is primarily due to the high labour content of interview surveys. A comparison of costs between persona interview and self-completion appears in Ampt and Richardson (1994).

(b) In order to reduce travel expenses and interviewer lost-time, many household-based personal interview surveys make use of clustering of households or survey sites on a geographic basis. This causes the "effective sample size" to be reduced with consequent reductions in the accuracy of estimates from the data.

(c) The interview situation is basically a human interaction between an interviewer and a respondent. Such interactions are rarely, if ever, completely neutral. The resulting interaction (often termed interviewer

bias) may affect each participant (and the data which is collected) in

various ways including:

(i) The personal characteristics of the interviewer (e.g. age, sex, nationality, general appearance) may influence the answers because of the impression made by the interviewer on the respondent (and vice versa).

(ii) Respondents are being asked to disrupt their normal routine in order to answer the interview questions. If such a disruption is inconvenient, this may distort the answers given by

respondents (if, for example, they wish to return to their normal routine as soon as possible).

(iii) An interviewer with strong opinions may subconsciously communicate these opinions to the respondent by the way in which the questions are asked or the answers are received. In some circumstances, some respondents may agree, or disagree, with statements depending on their perception of the

temperament of the interviewer.

(iv) Answers to questions early in the interview allow the

interviewer to build up a picture of the respondent's general behaviour and attitudes. The interviewer may then interpret later answers (especially vague answers) to be consistent with this picture even though the respondent may have intended to give a contradictory or apparently inconsistent answer.

Alternatively, the interviewer may construct a picture of the type of person being interviewed (based, for example, on socio- economic characteristics of the respondent) and then interpret vague answers to fit within an idea of the expected response from that type of person.

(d) Personal interview surveys are not suited for situations where questions require a considered response, or where factual information is required which is not immediately available. The time delay involved in obtaining such responses is either a waste of the interviewer's time, or else the respondent feels embarrassed at making the interviewer wait for the answer.

In summary, personal interview surveys are best for attitude surveys, for surveys where the concepts are complex or where there is a complex series of sequencing required. They are more expensive than their self-completion counterparts and have to be designed thoroughly to minimise interviewer bias, but their high response rates and their ability to be carried out within a relatively short time interval make them ideal in cases where high quality data is required within a medium time frame.