Even though attrition presents a serious threat to the validity of longitudinal research, there is a lack of standardization for reporting it. To examine the effectiveness of four tests for attrition -- two for external validity and two for internal validity -- the tests were applied to two large scale projects: the first, Project HASP, is a…

Longitudinal studies conducted with children typically experience non-response problems that can make substantial inroads on sample size and introduce bias into the analysis. Three methods for limiting non-response in school-based research programs were assessed: (1) asking parents to return consent forms only if they do not want their children to…