When it is important to explore a subject in detail or probe for latent attitudes and feelings, the in-depth interview may be the appropriate technique to use. Depth interviews are usually conducted in person, although telephone depth interviewing is slowly gaining greater acceptance.
With the approval of the respondent, the interview is audio taped, and may even be video-taped, in order to facilitate record keeping. Although it is a good idea to prepare an interview guide ahead of time to be sure to cover all aspects of the topic, the interviewer has significant freedom to encourage the interview to elaborate or explain answers. It is even possible to digress from the topic outline, if it is thought to be fruitful.
Interviewers must be very experienced or skilled, since it is critical that s/he and the respondent establish some kind of rapport, and that s/he can adapt quickly to the personality and mood of the person being interviewed. This will elicit more truthful answers. In order to receive full cooperation from the respondent, the interviewer must be knowledgeable about the topic, and able to relate to the respondent on his/her own terms, using the vocabulary normally used within the sector being studied. But the interviewer must also know when it is necessary to probe deeper, get the interviewee to elaborate, or broaden the topic of discussion.
Since an interview can last anywhere from 20 to 120 minutes, it is possible to obtain a very detailed picture about the issues being researched. Even without considering the potential from interviewer bias, analyzing the information obtained requires great skill and may be quite subjective. Quantifying and extrapolating the information may also prove to be difficult.
Related Readings (Kumar, V., Aaker, D.A. & Day, G.S. (1999). Essentials of Marketing Research. New York: John Wiley & Sons, Inc.; Zikmund, W.G. (1997). Exploring Marketing Research, 6th edition. Orlando: The Dryden Press)