An in-depth interview (frequently abbreviated as IDI’s) is a form of qualitative research; a somewhat intensive individual conversation exploring opinions and perspectives on an idea, product, market or other topics. They are discussion-oriented and free-flowing, moving easily from one question to the next, allowing the respondent to dictate the flow and pace of the conversation. IDI’s are often used to provide context to a larger-scale survey, offering a more complete understanding of the topic.

Questions are open-ended, not allowing the respondent to answer with a single word answer. Should respondents provide a brief answer, a skilled interviewer will probe to understand the root cause or driving force behind the response. The interviewer will also ensure that the question is answered completely and is consistent with answers to other, related questions in the conversation.

Interviews are conducted with individuals that are selected for their expertise, experience, position at certain companies or organizations, or knowledge of a topic. A typical project incorporating IDIs would include between 10 and 100 completed interviews. PMG has found that consistent responses tend to emerge after 10 interviews in a segment, and after 25 interviews in a segment, the point of diminishing returns is reached.

A highly skilled and experienced interviewer is required to convince someone to participate in a discussion, set an appointment, and then complete the interview gathering detailed and complete answers to most questions. Good interviewers are also adept at listening for clues in the tone, word choice, and phrasing of responses – and using those clues to phrase follow-up questions.

Advantages and Drawbacks of using and IDI

The primary advantage of in-depth interviews is that they provide much more detailed information than what is available through quantitative surveys. Because a good interviewer will establish a rapport with a respondent, articulate and insightful responses are frequently obtained.

Drawbacks of IDI’s include the potential for bias, since relatively few interviews are normally completed. Also, interviews can be lengthy, however, PMG recommends that an IDI be able to be completed within 15 minutes to have a reasonable chance of success. The actual interview may take much longer, but some key respondents may have limited time. Of course, since IDI’s are qualitative, the results normally cannot be generalized. This is not always the case in a B2B setting, as some market segments are very small.