The recruitment process was completed for each of the three annual cohorts, resulting in a total sample size of 360 parent-child pairs. Of the 360 children enrolled in the RCT, 71.4% (n = 257) provided a DNA sample that was successfully genotyped for rs2268493. Of this sample, 197 participants self-reported as African-American and 60 identified as Caucasian, Hispanic, or other (Figure 1). In this study we did not have the resources available to test the DNA for markers of genetic ancestry. Thus, in order to minimize the possibility that results could be affected by population stratification, or the fact that there are differences in allele frequencies between subpopulations due to different ancestry, we limited the analyses in the present study to the subsample of African-American participants. It should be noted that this solution does not entirely address the issue of population stratification, as there is still the possibility of population stratification within the African-American subsample (see Limitations).
