Am I My Brother's Barkeeper? Sibling Spillovers in Alcohol Consumption at the Minimum Legal Drinking Age

We use data on siblings near the minimum drinking age to provide causal estimates of peer effects in alcohol consumption, exploiting the increase in consumption of the older sibling in a regression discontinuity design. Preferred point estimates imply that younger sibling binge drinking decreases at the cutoff. These negative reduced form spillover effects are concentrated in subgroups where the first stage discontinuity is largest, among siblings who are likely to spend more time together, and for measures of excessive alcohol consumption. While our results are somewhat imprecise, we argue that these patterns of heterogeneity are consistent with younger siblings learning from the costs of their older siblings' drinking behavior. Our results are directly interpretable as the effect of peer alcohol consumption, whereas most prior work identifies the effect of exposure to the peer. We explain how this distinction matters for policy.