Tracking non-traditional populations in longitudinal studies

Methods used to track a panel of 670 homeless substance abusers over 3, 6, and 12 month intervals are described and results suggest that a broad brush tracking strategy with emphases on telephone, mail and field tracking served to minimize panel mortality and its accompanying methodological problems.

Abstract

As health services research focuses on prevention and drug treatment programs for special populations, maintaining panel samples at adequate levels over time becomes more important. Differential panel mortality poses a serious threat to the internal validity of experimental designs and the external validity of study conclusions. Minimizing respondent attrition demands systematic attention to two problems: location of subjects at each wave and sustaining respondent cooperation over the life of the research. Major obstacles to collecting longitudinal data on non-traditional populations include the inapplicability of most community-based and governmental records, inexperience with tracking those without stable addresses, and cost. This paper describes and evaluates methods used to track a panel of 670 homeless substance abusers over 3, 6, and 12 month intervals. Results suggest that a broad brush tracking strategy with emphases on telephone, mail and field tracking served to minimize panel mortality and its accompanying methodological problems.