Limiting Nonresponse in Longitudinal Research
Three Strategies for School-Based Studies
Longitudinal studies conducted with children typically experience nonresponse problems that can make substantial inroads on sample size and introduce bias into the analysis. This Note describes and assesses three methods for limiting nonresponse in school-based research programs: (1) asking parents to return consent forms only if they do not want their child to participate in the research, (2) conducting make-up sessions for students who are absent during the scheduled data collection, and (3) tracking students who transfer out of participating schools. These methods were used in a large-scale, longitudinal study designed to assess the effects of a smoking- and drug-prevention curriculum for adolescents across 30 schools in California and Oregon. Each method substantially reduced the anticipated loss of participating students over a two-year period; each also reduced attrition bias attributable to the loss of at-risk students — those with characteristics such as poor grades, prior deviance, and past drug experience that make them likely candidates for using drugs in the future.