Step 6: Limit the number of questions to a set that can be covered within 60 to 90 minutes.

Experienced interview researchers (see references) suggest that ideally an interview lasts 1 to 2 hours. Allocating less than an hour runs the risk of making the interviewer and respondent feel rushed and unable to develop full rapport. Exceeding 2 hours runs the risk of fatiguing both interviewer and respondent. Thus, we recommend planning a set of main questions that, allowing for prompts, will take between 60 and 90 minutes to cover. This way, even with the possibility of unexpected interruptions or overruns, the interview would not exceed 2 hours.

The number of questions you can include depends on their type. In the case of a more structured interview composed entirely of open-ended, topic-focused questions for which you anticipate fairly detailed answers, it probably is wise to allocate an average of 3 minutes per question. Thus, an hour-long interview could consist of up to 20 questions. Several more questions could be added to the set if they are short information or closed-ended questions. If the interview is less structured, asking the respondent to recount events or perspectives that may take each interview in different directions, the number of questions should be cut considerably. Pilot-testing the interview will confirm whether the number of questions is appropriate for a given time frame (see next step).

Logistical considerations also play into planning the length of an interview. When interviewing respondents in a work environment, there may be serious time limits. If you know that respondents will not have a block of time approaching 1 hour, it is worth considering whether another evaluation tool might better suit your purposes. Also, it is reported (Seidman, 1991) that a 90-minute interview takes from 4 to 5 hours to transcribe and generates approximately 50 pages of transcription (see Administering Interviews). In short, before embarking on an interview, you need to be sure you have the resources to transform the interview into usable information.