role of each correlated phenotype as an exposure and intelligence as the outcome. For each trait, we selected independent (r2=<0.1), GWS lead SNPs as instrumental variables in the analyses. For traits with less than 10 GWS lead SNPs (i.e. the minimum number of SNPs on which GSMR can perform a reliable analysis), the GWS threshold was lowered to 1×10−5, allowing a sufficient number of SNPs to conduct the reverse GSMR analysis for former smoker status, autism, and intracranial volume.
