Of the families who provided data at the pretest assessment, 91% provided data at the long-term follow-up assessment conducted 29 months after the pretest. Two years after the long-term follow-up (4.5 years after the pretest), we attempted to re-contact the study families to obtain youths’ DNA from saliva samples. Of the original sample assessed at pretest, 84% (n = 539) of the families were relocated; in the relocated families, 86% (n = 461) of the youth agreed to provide DNA. Two equivalence analyses were executed to determine whether any differences existed on demographic characteristics (monthly per capita income; number of children in the household, target gender, and maternal marital status) or the study variables (frequency of past-month alcohol use, marijuana use, and sexual intercourse) between (a) the families with pretest data and the sample with long-term follow-up data and (b) the families of target youth who did (n = 461) and did not (n = 78) agree to provide DNA (to conserve space, the means and standard deviations for these tests are not presented). For these analyses, t tests were
