We constructed a linkage disequilibrium (LD) map using Haploview software, Version 4.1, from which we defined haplotype blocks. We constructed the blocks using the method of Gabriel et al. (2002) but modified it to include SNPs for which D′ = 1 regardless of lower confidence bound. Haplotypes that were observed fewer than five times were dropped from the analysis. We also checked that LD estimates were similar between our data and those of the HapMap CEU sample (i.e., Utah residents with Northern and Western European ancestry from the CEPH [Centre d’Etude du Polymorphisme Humain] sample). Using PLINK, we tested each haplotype within each block of DRD2 for association with stop RT, go RT, and ZKPQ Impulsivity/Sensation Seeking subscale scores. We empirically assessed statistical significance while accounting for the testing of multiple haplotypes in each block separately using 5,000 permutated datasets.
