Personal interviews or face to face interviews as they are often called, are of two distinct types – interviews at the respondent’s home (door-to-door) and interviews elsewhere, primarily by regional shopping centers (mall intercepts).
The number of market researchers using the mall intercept method to collect survey data has increased tremendously in the last few years. Rising costs associated with door-to-door interviewing have found many market researchers conducting face-to-face interviews in central locations, typically in regional shopping centers. Approximately 169 permanent market research facilities are located in enclosed shopping centers across the United States.
Mall intercepts and door-to-door interviewing have many of the same advantages and disadvantages. The following discussion will focus on personal interviewing as a general category; but where there are differences between the two types.
A direct comparison of the quality of information obtained in mall intercepts compared to telephone interviews showed there is no difference between the two on completeness of answers to questions or on refusal to answer certain questions; but there was a significant difference in reporting on socially desirable behavior (subscribing to a newspaper, voting in the last election) and socially undesirable behavior (receiving a speeding ticket) Contrary to expectations telephone interviews showed a higher proportion of desirable behavior and a lower proportion of undesirable behavior.
As already indicated, the personal interview is the most versatile and flexible of the three communication method. Projects involving the use of props such as product samples or copies of advertisements or those that require the interviewer to make observation at the time of the interview are almost limited to the use of personal interviews. Unstructured questioning and long, difficult questionnaires are more effective when handled by personal interviews. Shopping center interviewing, particularly when the research organization has a ‘store’ in which to conduct the interviews is particularly advantageous when the interviewer needs to show things as in package evaluations., taste tests, and advertising pretests.
During the interview itself, the presence of the interviewer permits flexibility in procedure. The questioning can be adapted to the situations, further explanations or clarifications can be requested if desired mechanical aids or displays can be used. Also sets of cards can be given to the respondent for sorting. The respondent can be questioned on the brands in the pantry.
Unfortunately, these advantages of the personal interview tend to be offset by the high cost of door-to-door interviewing and by sampling problems in shopping center interviewing. Interviewing respondents in shopping centers reduces the costs compared with home interviews but makes it impossible to control the sample in a way desired for many studies. Even the flexibility inherent in personal interviews is not as advantageous as it seems. Relatively little advantage is taken of the possibilities because variations by interviewers may vary the results.
A further advantage to using personal and telephone interviews is that projects can be stopped or altered at any point during the study. Such is not possible with a mail study. Once questionnaires are mailed, the study is committed and the sample or the questionnaire cannot be changed.
Information Obtained: Both quantity and quality if information obtained are important. Most commercial research organizations operate on the assumption that long questionnaires (i.e. large quantities of data) can best be handled by personal interview, next best by mail, and least well by telephone. Although this is a sound principle there is increasing evidence that the latter two are less limited in length than has been assumed. The University of Michigan Survey Research Center, however, limits its telephone interviews to 11 minutes in length; personal interviews may run to 75 minutes. The time that an interview can run, however is determined at least as much by the clarity of each questions, the perceived relevance to the topic, and the lack of redundancy as by the method of communication.