(A) Graph of pairwise r² measures of LD among the 14 high-frequency (>6%) ABCB1 SNP loci described in Table 1. (B) r² for 3435C>T against each of the remainder SNPs, together with Bayesian 95% credible intervals calculated by the method described in the Supplemental materials. The dashed box identifies the high-LD interval around 3435C>T. All sites upstream of IVS 27+1220 show association with 3435C>T, significant at the 0.001 level (Fisher's exact test). At the loci downstream of this site, we observe no significant association (P > 0.05) with 3435C>T. Throughout the study we used r² to measure association, to take into account the dependency of LD on allelic frequencies. (C) Graph of posterior odds of each SNP being causal relative to 3435C>T being causal, based on the combined LD data and case control data on 3435C>T (Siddiqui et al. 2003), using the method described in the Supplemental materials.