Conducting Follow-Up Interviews With Offenders: How MNany Respondents Are Needed? At What Cost?

Michael Prendergast, University of California at Los Angeles
Elizabeth Hall, University of California - Los Angeles

In planning and budgeting for follow-up studies that include individual interviews, researchers must balance their desire to interview as many subjects as possible against the high costs involved in tracking and locating as a high percentage of subjects. How many more follow-up interviews are necessary to reduce possible bias to an acceptable level? What are the average and marginal costs of conducting follow-up interviews? Do hard-to-find subjects differ from easy-to-find subjects in their characteristics and their outcomes? At what point should locating subjects for follow-up interview stop? Are there guidelines that can guide the decision? Using information on tracking logs used in a five-year follow-up study of participants in an evaluation of a prison-based drug treatment program, we describe the study's tracking and locating procedures, develop profiles of hard-to-find and easy-to-find subjects using cluster analysis, and present data on differences in outcomes by tracking status. In addition, we identify the costs associated with tracking, locating, and interviewing subjects for follow-up, and cost out different types of follow-up studies. Possible ways to reduce follow-up interview costs will be discussed.

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Updated 05/20/2006