Face-to-face interviews are a direct communication, primary research collection technique. If relatively unstructured but in-depth, they tend to be considered as part of qualitative research. When administered as an intercept survey or door-to-door, they are usually part of quantitative research.
The opportunity for feedback to the respondent is a distinct advantage in personal interviews. Not only is there the opportunity to reassure the respondent should s/he be reluctant to participate, but the interviewer can also clarify certain instructions or questions. The interviewer also has the opportunity to probe answers by asking the respondent to clarify or expand on a specific response. The interviewer can also supplement answers by recording his/her own observations, for instance there is no need to ask the respondent’s gender or the time of day/place where the interview took place.
The length of interview or its complexity can both be much greater than in other survey techniques. At the same time, the researcher is assured that the responses are actually provided by the person intended, and that no questions are skipped. Referred to as item non-response, it is far less likely to occur in personal interviews than in telephone or self-administered surveys. Another distinct advantage of this technique is that props or visual aid can be used. It is not uncommon, for instance, to provide a written response alternatives where these are complex or very numerous. Also, new products or concepts can be demonstrated as part of the interview.
Personal interviews provide significant scope for interviewer error or bias. Whether it is the tone of voice, the way a question is rephrased when clarified or even the gender and appearance of the interviewer, all have been shown to potentially influence the respondent’s answer. It is therefore important that interviewers are well trained and that a certain amount of control is exercised over them to ensure proper handling of the interview process. This makes the interview survey one of the most costly survey methods.
Although the response rate for interviews tends to be higher than for other types of surveys, the refusal rate for intercept survey is higher than for door-to-door surveys. Whereas the demographic characteristics of respondents tend to relatively consistent in a geographically restricted area covered by door-to-door surveys, intercept surveys may provide access to a much more diversified group of respondents from different geographic areas. However, that does not mean that the respondents in intercept surveys are necessarily representative of the general population. This can be controlled to a certain extent by setting quota sampling. However, intercept surveys are convenience samples and reliability levels can therefore not be calculated. Door-to-door interviews introduce different types of bias, since some people may be away from home while others may be reluctant to talk to strangers. They can also exclude respondents who live in multiple-dwelling units, or where there are security systems limiting access.