In-depth interviews are an informal individual discussion, carried out according to a well-organized timely screenplay, that would influence the respondents to long and argumentative discussions on interesting questions of the researcher. In-depth interviews are used to delimit the problem and proposing hypotheses, and to identify basic indices before quantitative research. Because of the limited number of respondents, the results can not be generalized to the entire population.
The interview is conducted one to one without the presence of third persons and comprises 30 to 60 minutes. Making an in-depth interview requires very high skill of the interviewer as there is an increased possibility of influence of subjective attitude of the interviewer to final outcome of the research. The interviewer must collect all the details and meanwhile not to deviate the respondent from his mind.
During a research usually is carried out not less than 20-30 in-depth interviews.