Final answer:
The professional interviewer is conducting a depth interview, which is an in-depth qualitative research technique that allows an interviewer to thoroughly explore a respondent's views on a certain topic, in contrast to broader surveys or case studies.
Step-by-step explanation:
A professional interviewer holding a 90-minute discussion with one member of the target market to find out why that respondent purchases a particular brand of clothing is conducting a depth interview.
A depth interview is a qualitative research technique that involves conducting intensive individual interviews with a small number of respondents to explore their perspectives on a particular idea, program, or situation. This approach is in contrast to surveys, such as a case study or survey method, which might involve predefined questions posed to a larger number of respondents.
The key feature of a depth interview is its ability to probe deeply into a respondent's feelings, beliefs, or thoughts, providing a comprehensive understanding of the individual's perspective on the subject matter.