We acknowledge limitations. First, our analysis was based on a small sample. Only 242 European-American and 248 African-American Fast Track participants met inclusion criteria. Replication is needed. Nevertheless, use of a randomized controlled trial increases power and bolsters confidence that results are not confounded by unmeasured correlations between genotype and environment (McClelland & Judd, 1993; Fletcher & Conley, 2013). A specific feature of the Fast Track design that may increase power is the focus of the trial on very high-risk children among whom rates of adult externalizing psychopathology absent treatment were expected to be high. This expectation proved correct. By age 25 years, the majority of children in the control condition manifested externalizing psychopathology. A second limitation of our data is that we did not observe the complete sequence of the NR3C1 gene. Instead, we observed a set of tagging SNPs identified from reference data. Further analyses in additional samples are needed to identify the causal sequence that is the source of the signal detected at rs10482672. Third, it is uncertain whether results generalize to non-white populations. To the extent
