The allele and genotype frequencies for DRD4 are provided in Table 1. The distributions of the allele and genotype frequencies, and the short-long genotype classification are consistent with prior research with Caucasian and European samples (Hutchison et al., 2003; van der Zwaluw et al., 2012) as well as with European samples reported in the Allele Frequency Database (Rajeevan et al., 2012). We did not collect data on ancestry informative markers and relied on self-reports of ethnicity. Because the frequency of the DRD4 7-repeat allele may vary considerably across world populations (Kidd et al., 2014), and a small percentage of our sample was of non-European origin, we conducted the subsequent data analyses with and without the small subsample; results were not altered and therefore the results subsequently reported on are based on the full sample size of 340.
