Am I My Brother’s Barkeeper?

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. We find no evidence for positive spillover effects of an older sibling’s legal access to alcohol on the younger sibling’s alcohol consumption. Although imprecise, preferred point estimates imply that younger sibling binge drinking decreases at the cutoff. These negative reduced-form spillover effects are larger for siblings who are likely to spend more time together, for measures of excessive alcohol consumption, and in subgroups where the first-stage discontinuity is largest. We argue that these patterns of heterogeneity are consistent with younger siblings learning from the costs of their older siblings’ drinking behavior.