Given differential rates of genetic recombination, allele frequencies and linkage disequilibrium (LD; an estimate of the degree of association between SNPs) often differ across populations. Thus, we limited all analyses and data reported in this paper to the European American subsample to guard against the introduction of bias via population stratification. Haploview (Barrett et al., 2005) was used to estimate LD across the nine genotyped SNPs. As in previously genotyped samples, pairwise associations between markers in CHRM2 were moderate to high (see Table 1), yielding R2 values ranging from 0.22 to 0.98. Likewise, D′ (an alternative estimate of association that is less sensitive to variation in allele frequencies; Hedrick & Kumar, 2001) values ranged from .63 to 1.00. Together, these measures of association suggest at least modest correlations between all nine SNPs; thus, analyses with individual markers do not represent independent tests of association.
