Panel Attrition and External Validity in Adolescent Substance Use Research.

Examined seven-year adolescent panel to determine whether attrition effects varied by type of substance assessed and method of measurement. Found 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 that use-nonuse comparisons. (Author/NB)