Next, we added baseline HED and AP levels to each model to statistically control for their effects, in order to examine whether the individual and situational factors uniquely contributed to improved group membership above and beyond the influences of baseline HED and AP. Thus, including these covariates enabled us to infer predictors of change that were not confounded with pre-intervention drinking levels. In other words, we examined, given the same levels of HED and AP at baseline, whether the individual and situational factors predicted improved group membership. When we adjusted for baseline HED and AP (see the middle column in Table 3), we found that experiencing a serious incident, reporting greater readiness to change, being female or a non first-year student, and reporting no other drug use significantly predicted improved group membership. Baseline AP and positive alcohol expectancies no longer significantly predicted improved group membership. Positive alcohol expectancies and AP at baseline may largely be accounted for by baseline HED. Interestingly, greater readiness to change was a significant predictor of improved group membership only after baseline HED and AP levels
