Subject Attrition in Prevention Research

Experimental evaluations of substance use prevention programs are hampered by high rates of subject attrition. Attrition threatens the internal validity of these studies when attrition is greater in one condition than another. Statistical tests of the effects of attrition are typically lacking. Attrition threatens the external validity of studies because one may not be able to generalize effects of programs to dropouts who are systematically different from those who remain.