Panel attrition and external validity in adolescent substance use research.

Panel attrition threatens external validity in adolescent substance use research. A 7-year adolescent panel was examined to determine whether attrition effects varied by (a) type of substance assessed and (b) method of measurement and type of statistical analysis. Chi-squares and multivariate analyses of variance revealed that study dropouts were more likely to use substances and reported higher mean use of substances at baseline than stayers; attrition effects varied by substance; and mean use comparisons were more likely to detect attrition effects than use-nonuse comparisons. Implications of these findings for adolescent substance use research are discussed.