Kotler et al. [60] investigated the association between novelty seeking and long repeat alleles of DRD4 and found a significantly increased number of the 7-repeat allele in 141 male opioid dependent subjects (29.1%) compared to 110 male controls (11.8%), (χ2 = 10.9, d.f. = 1, P = 0.00096). To account for ethnic variations, which may confound the findings of a population’s allele frequencies, the frequency of the 7-repeat allele was compared within the two ethnic groups that were studied. There was an increased number of long alleles within the opioid-dependent Israeli Arab cohort (χ2 = 5.05, d.f. = 1, P = 0.024) and the Sephardic Jewish opioid-dependent cohort (χ2 = 5.01, d.f. = 1, P = 0.023), without any significant differences noted between the two demographic populations [60].
