To determine the contributions of interview age, sex, and ancestry, these variables were included in the new models as covariates. Ancestry was determined through the use of a set of 64 ancestry informative markers (AIM), which were genotyped as part of a 96 SNP Biorepository Panel by the Rutgers University Cell and DNA Repository. SNPrelate, a library function in R (R Development Core Team, 2013), was applied to these markers to estimate principal components in order to assign ancestry groups at family and individual levels. HapMap3 populations were included as reference groups. Based on the first two principal components, individuals were assigned to one of three ancestry groups: EA, AA, or Other. Seventeen subjects were assigned to the “Other” group; due to its small size, this group was removed from further analysis. This resulted in a final sample size of 674 subjects, with 451 (66.9%) identified as EA and 223 (33.1%) as AA. There were no significant differences with respect to gender, interview age, or predictor scores for subjects with genotype data (674) and those who were dropped (146).
