Genotype imputations reported here were conducted using MaCH, unless otherwise stated (Li et al. 2010). As other studies have done, (Shriner et al. 2010; Southam et al. 2011; Howie et al. 2011) we focused on a single chromosome (chromosome 22) for efficiently evaluating imputation performance. Imputation across genotyping arrays may be conducted separately within each originating study or with all study subjects combined. Here, we report results from separate imputation in each of the eight originating studies of European Americans or African Americans (Table 1). Similar results were found from imputations conducted using all study subjects combined (results not shown).
