Study limitations are noted. First, all responses are based on self-report, which is known to have error. However, we used current time frames for all analyses, limiting the effect of recall bias. However, differences in norms around drinking could lead to differential under-reporting, especially as Blacks in the US attach higher stigma to individuals perceived to have alcohol problems compared with Whites (Keyes et al., 2010a). Second, there was substantial attrition over the four waves of the study, and more attrition among Whites than among Blacks. If substance users were more likely to be lost to follow-up, which we would expect, then the sample is missing more White substance users. Thus, again, we would expect the results to be underestimated. Third, there are sizeable gaps between data collection periods, thus nuance in lifecourse associations from a year-to-year basis may be missed when relying on four data-points across two decades of development. Nonetheless, the Add Health study is a landmark study about population-based longitudinal study of development, with national representativeness and a large, diverse sample. Thus, the limitations of misclassification and informative losses-to-follow-up do not outweigh the substantial strengths of the study.
