Genotype control data were obtained from the Wellcome Trust Case Control Consortium–Phase 2 (20). They comprised 3,000 individuals born in the United Kingdom during 1 week in 1958 (the 1958 British Birth Cohort) and 3,000 individuals from the U.K. Blood Services collection. It has previously been shown that it is valid to combine these two samples for use as comparison subjects in genetic association studies using U.K. case samples (20). The comparison subjects were not screened for psychiatric disorders. However, the potential loss of power that is attained by using unscreened comparison subjects is more than offset by the large numbers of comparison samples available (21).
