The PLINK meta-option reports the Cochrane’s Q statistic as a measure of heterogeneity for each SNP. One significant heterogeneity P-value was obtained for SNP rs588765 (P = 0.01) in the AOS analysis only. It is unlikely this heterogeneity can be accounted for by differences in phenotype assessment between studies because this would be predicted to result in significant heterogeneity for all loci in the AOS analysis. Large differences in allele frequencies between groups could also produce heterogeneity. Examination of allele frequencies for all participating groups suggests one outlier (NTR1 T allele frequency is 0.9) within this SNP/locus. In order to determine whether this sample population was driving the significant Q statistic for rs588765 and AOS, the meta-analysis was performed excluding this sample. Results for AOS were similar and the Q statistic P-value was identical (beta = −0.004, P = 0.281, Q P-value = 0.01) suggesting the NTR1 rs588765 T allele frequency is not the cause of observed heterogeneity at this locus. Furthermore, results from a random effects model (automatically generated by PLINK) were nearly identical for rs588765 (fixed effects beta
