We observed that the test statistic for association from the meta-analysis, but not the individual cohort analyses, was inflated for both gf and gc (Figures 1 b,d and Supplementary Figures 4,6). Inflated test statistics are indicative of either population stratification or polygenic variation. There was no strong evidence of population stratification within each of the five discovery cohorts (Supplementary Figure 2). Moreover, four multi-dimensional scaling (MDS) components were fitted in each individual cohort analysis to account for the effects of possible subtle population stratification. Therefore, we reasoned that the inflation of the test statistic across the genome was indicative of polygenic variation.
