Voxel-based analysis of covariance (ANCOVA) was used to detect effects for each of the 4 SNPs on gray matter volume (modulated images) and gray matter concentration (unmodulated images) (4). ANCOVA was performed to explore the group differences in hippocampus morphology across ethnic groups (EAs, AAs, Asian and other) in order to confirm if there were differences among the populations. Age and sex were included as covariate in these analyses. For a priori hypothesis testing, findings were considered significant at P<0.005 uncorrected for multiple comparisons and spatial extent of 25 voxels. Data were also inspected for survival for conservative Bonferroni correction for study of four SNPs which required a P-value of 0.00125. Whole brain analyses were performed to explore for potential effects in gray matter regions that we did not hypothesize a priori, with significance assumed at P<0.0125, corrected for multiple comparisons with false discovery rate, and extent threshold of 25 voxels.
