We assess the extent to which the large sibling correlations in substance use are causal. Our primary approach is based on a joint dynamic model of the behavior of older and younger siblings that allows for family specific effects, individual specific heterogeneity, and state dependence. We use the model to simulate the dynamic response of substance use to the behavior of the older sibling. Overall, we find that substance use is affected by the example of older siblings, but only a small fraction of the sibling correlation is causal.
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