Our results could potentially have differed had abstainers been coded as missing rather than as ‘0’. Addressing this possibility is not entirely straightforward, as participants reporting an average consumption of no drinks for an epoch were not necessarily abstaining entirely: their consumption could simply have been too low to differ substantially from 0 from their perspective. However, we made an effort to explore the possibility by recoding potential abstainers as missing. Model-fitting procedures produced a qualitatively similar final model, with two A factors and one C factor, though model fit statistics were far less satisfactory (results available upon request). The relative contributions of each A factor to total heritability were also similar, with one factor primarily influencing very early drinking and the other influencing consumption in early to mid-adulthood. The most pronounced difference under the recoding scheme is that the total h2 of consumption in epochs 1 and 2 was higher than reported here, at about 0.20 for each time point. These estimates are based on quite small samples of early adolescents who drink, and the CIs are wide and
