The structure of the genome differs across ethnic groups (International HapMap Consortium, 2007) and these differences can confound genetic association analyses (Cardon & Palmer, 2003). Briefly, allele frequencies vary between populations separated in human evolutionary history. These differences can give rise to spurious genetic associations in the case that the outcome of interest is unequally distributed across ethnic groups within a sample. This problem is conventionally referred to as “population stratification” in the genetics literature; an accessible discussion of this issue can be found in Hamer & Sirota (2000). We address this issue in our sample, which included both African-American and white children, by conducting analyses separately within ethnically homogenous groups.
