We conducted sensitivity analyses to see whether effects changed when using a more conservatively defined subsample of siblings who were known to have the same living arrangements while growing up or who were born within 3 years of the eldest. These more conservative definitions assume that siblings who report the same living arrangements growing up and who are born in closer proximity to one another are likely to share more features of their home environment than siblings who report different living arrangements or who are born further apart. In total, 1702 individuals (54% female) from 739 sibling groups were available for this analysis. We also examined whether the effects were robust when sibships that included monozygotic twins (8 sibling groups) were removed from the analysis. Monozygotic twins share 100% of their genetic variation, and we wanted to ensure that our results were not driven by genotyping errors or PLINK’s handling of SNPs set to missing (as part of cleaning for Mendelian errors) during polygenic score calculation. Sample size as a function of the filters employed for these sensitivity analyses are shown in Supporting Information Figure 1.
