The current study uses data from the Prospective Study of COGA, which consists of 3,444 offspring or relatives of the probands and control families from the original COGA study, followed biennially since 2004. Data collection is on-going, although 33% of the study sample had been assessed 4 or more times as of 2013 (63% had >3 assessments). Of those 3,444 individuals, only a subset had GWAS data (n=412). Furthermore, only participants of European descent were initially genotyped in order to avoid confounds due to population stratification. See Table 1 for demographic information of the Prospective Study GWAS subsample.
