Power calculations were performed using the Genetic Power Calculator (Purcell et al., 2003) (http://pngu.mgh.harvard.edu/~purcell/gpc). Given a prevalence of unipolar depression of 16% (Kessler et al., 2003), a marker in LD (D′=1) with a risk allele R and an alternative protective allele N under an allelic log-additive, dominant or recessive model and 80% power in our discovery genome-wide study at a significance level −7 (=0.05/365,676 SNPs ), we would be able to detect an effect with an OR of 2.2 or larger.
