In addition to rAOS, we incorporated several other variables to examine the specificity of smoking onset age and to examine whether changes in model fits might be due to modeling artifacts. These included permuted rAOS, to simulate the null hypothesis with respect to the interaction – that is, individual rAOS values were randomly re-assigned to other individuals in the data set. This is labeled “pAOS.” Other moderators, that are correlated with rAOS but which were not hypothesized a priori to have moderating effects were age at first cigarette (rAFC), age at first drink (rAFD) and age at onset of drinking (rAOD). Strong results for these alternative moderators might indicate that a more general behavioral factor is involved in the interaction, as opposed to tobacco use.
