Here are some basic rules of thumb when deciding how many people need to be involved in interviewing:
number of interviews = number of weeks X number of interviews done at the end of the project done in one week number of interviews = number of interviewers X number of done in one week interviews done by one interviewer in one week
In projects I've worked on, one interviewer can do about three interviews per day, or about twelve-fifteen per week. This may seem low, but it is always best to assume that fewer interviews will get done than one might think. The average of three includes days when interviewers do five, and other days when they conduct only one. There are always delays as interviewers try to find the complainants, as interviewers take longer to finish work on questionnaires, and as interviewers emotionally burn out under the stress of hearing such traumatic stories.
Say, for example, that an organization wants to do 5,000 interviews. They have forty interviewers available, and from experience they estimate that each interviewer can do about twelve interviews per week. At this rate the interviewers together will do 480 interviews per week, which means that with minor delays, the project's interviewing step will take about eleven weeks (5000 interviews/480 per week) to complete.