Scores for the physical discipline risk factor ranged from 0–19, out of a possible 24. The mean score for the sample was 3.02±0.247, with a median score of 2. To test for gene-environment correlation, we assessed whether genotype classes differed significantly in their level of physical harm, and found that they did not (r=−0.004, p=0.977): the mean score for those carrying the high-activity allele was 3.00±0.334, and for those carrying the risk (low-activity) allele the mean was 2.98±0.499. Furthermore, there were no differences between genotyped and non-genotyped individuals in physical discipline score (F=0.031, p=0.861), overall externalizing behavior (F=1.125, p=0.290), aggressive behavior (F=1.105, p=0.315), or delinquency (F=0.503, p=0.479).
