In the primary analysis, we combined effects of each disease analysis by a meta-analytic approach that applied a weighted Z-score,18 in which weights equalled the inverse of the regression coefficient’s standard error. This strategy assumed a fixed-effects model, with weights indicating the sample size of the disease-specific studies. In a second analytical approach, we did a five-degree-of-freedom test by summing the χ2 values for each individual disease meta-analysis. Unlike our primary analysis, this model did not assume that all diseases had the same direction of effect and could detect allelic effects that increase risk for some diseases and decrease risk for others. The appendix describes statistical methods and results, including the handling of trios and population stratification. We also examined loci that previously achieved genome-wide significance in PGC meta-analyses of schizophrenia and bipolar disorder.6,7
