METAL (Abecasis, 2010) was used to perform meta-analysis of the results; it uses the weighted inverse variance method, computing a pooled effect estimate (ln(beta)), its standard error and its p-value by weighting the effect estimates of each cohort by the inverse of its variance and by incorporating the direction of effect. Automatic correction for any population stratification effects, if necessary, was done by applying genomic control, although individual cohort lambda values for each variable ranged between .97 and 1 (see Appendix CSupplementary Fig. 1 for genomic control inflation values for reported results). A chi-square test for heterogeneity tested whether the regression coefficients differed significantly between the cohorts contributing to the meta-analysis.
