Method  
This method involves interviewing one Respondent (less often two). The information obtained during the interview may be recorded on audio tape, but only with the consent of the Respondent. The idea of an in-depth interview is to get the Respondent to talk about a certain topic that he would not want to talk about in the presence of other people. During the in-depth interview, the Respondent can recognize the irrationality of his approach to purchases, which might not have been revealed during the formatted interview.

In which cases in-depth interviews are used: 

• When the topic of the study touches upon very personal views or may cause confusion when discussing in a group (for example, the use of deodorants, drugs, contraceptives, cosmetic problems);
• When the topic of discussion concerns the peculiarities of individual decision-making (for example, the purchase of any equipment);
• When the study group of people is a rare category of the population or it is problematic to bring respondents together at a certain time (for example, heads of large pharmaceutical companies).

Disadvantages of in-depth interviews: 
Duration (1.5 – 2 hours), but this disadvantage shall be compensated by the advantages of this method.

Procedure

In-depth interviews are face-to-face interviews according to a pre-planned plan, but in an informal form. In-depth interviews are flexible, which means that the wording and order of pre-planned questions may vary depending on the logic of the conversation and the topics covered during the interview.

Since the in-depth interview, as well as the focus group, belongs to the qualitative category of sociological research, it is possible to make serious conclusions with small arrays of the sample.