A meta-analysis of school-based substance abuse prevention studies revealed that the mean proportion of subjects retained dropped from 81.4 percent at the three-month followup to 67.5 percent at the three-year followup. Researchers should interpret their results in light of these normative data and adopt second-effort strategies to reduce…

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…