The effects associated with parental knowledge analyses showed greater dependency on the scaling of adolescent alcohol use. In the GxE models using the raw alcohol use frequency variable, we observed that parental knowledge moderated the additive genetic, shared environmental and unique environmental influences. However when using a non-linear square root transformed alcohol use variable, the moderating effects of genetic influences and shared environmental influences could be dropped in the model fitting procedure, though they still showed a trend (p = 0.06, p = 0.05) in the expected direction, whereby genetic and shared environmental influences increased under conditions of lower parental knowledge. While there is still a trend in the expected direction, the fact that the moderating effects in this case are affected by the distribution of the behavioral outcome may call into question the stability of the original findings in the raw variable (Lynch & Walsh, 1998; Mather & Jinks, 1982). Previously, using the same Finnish twin sample, Dick, Pagan, et al. (2007) reported moderating effects of parental monitoring on adolescent smoking but not drinking. Our analyses differed from those
