The biological function of rs279845 is not currently known, and there have previously been inconsistencies as to which rs279845 allele is associated with externalizing and alcohol-related outcomes, with some studies identifying the minor allele (A) as the risk allele (Dick et al., 2014; Lind et al., 2008; Uhart et al., 2013), whereas others have identified the major allele (T) as the risk allele (Dick et al., 2009, 2011; Edenberg et al., 2004). Thus, in the absence of clear prior information that could inform the choice of a genetic analytic model, preliminary analyses were run coding GABRA2 genotype as a dummy-coded categorical variable. The use of dummy codes allows a model-free approach that does not assume additive, recessive, or dominant genotype effects. Results of these preliminary analyses revealed that intervention effects for adolescents with AA and AT genotypes were highly overlapping; thus, these groups were collapsed into a single group (referred to hereafter as A carriers) and comparisons were made between adolescents with TT genotype and A carriers. This type of data-driven approach to genetic model specification has been taken in previous studies (e.g., Trucco, Villafuerte, Heitzeg, Burmeister, & Zucker, 2016).
