In the first set of sensitivity analyses, we examined whether effects held when the sample was limited to the groups of siblings who were known to have grown up together (N = 739 sibling groups). In the second set of sensitivity analyses, we examined whether the effects held when the sample was limited to those who were born within 3 years of the first born in a sibling group. In the third set of sensitivity analyses, we examined whether the effects were also robust when sibships that included monozygotic twins (8 sibling groups) were removed from the analysis. Across all three sets of sensitivity analyses in smaller, more conservative test samples, we continued to find that individuals with higher EduYears-GPS than their siblings had lower SUD criterion counts (Supporting Information Tables 4–6). The only exception to this was that the effect of sibling differences in EduYears-GPS on CUDSX was attenuated (P = 0.08) in the sensitivity analyses limited to those born within 3 years of the first born in a sibling group.
