There are also the usual problems associated with retrospective surveys, including social desirability and other possible reporting biases, limited information about the timing of law changes, but a particularly important concern is the lack of information about respondents’ state of residence at age 18. . Cross-state migration was common enough that it might have significantly affected our estimates; for example, if individuals at higher risk for alcoholism were more likely to have moved to a lenient-drinking-age state, then MLDA estimates based on current state of residence may overstate the effects of MLDA exposure on later outcomes. On the other hand, if cross-state migration wer uncorrelated with exposure status or other risk factors for alcoholism, then MLDA estimates based on current state of residence may have underestimated the full effect of MLDA exposure on later outcomes. In the NLAES sample, we found a statistically significant association between current alcohol or other substance use disorder and MLDA exposure calculated from state of birth; this provides a plausibly unbiased lower bound for our estimates, and suggests that selective migration cannot completely explain our results.
