therefore, these interchangeable SNPs were considered as a single marker in these analyses. These per-allele associations were pooled using a random effects method (44). Random effects models are typically more conservative than fixed-effects models, although in the absence of substantial between-study heterogeneity, the two methods generate similar results and generate identical results where there is perfect homogeneity. The I2 statistic was used to estimate the percentage of total variation in study estimates resulting from between-study heterogeneity. Conventionally, I2 values less than 25% are considered low and unlikely to represent important heterogeneity (45). The Cochran Q test was used to evaluate the statistical evidence for between-study heterogeneity.
