A question of interest is whether regular consumption of alcohol affected ERO values in our sample. To examine this the residuals from the non-parametric age regression of the log transformed ERO data were used in an ANCOVA. Subjects were divided into 3 groups: non-drinkers (N = 1148), drinkers from community families (N = 304), and drinkers from COGA families (N = 921). The continuous covariate was the difference between the age at test and the age at onset of drinking. In order to include the non-drinkers in this test, the difference values for them were taken from normally distributed random numbers with the same mean and variance as the difference values for the drinkers.
