That our effects remained for alcohol but not cannabis is in contrast to results reported by King et al. (2006), who found that alcohol use measures were unrelated to college degree completion after inclusion of predisposing factors, but that drug use slope remained significant. These differences could stem from a number of factors, including sampling and measurement. Whereas King et al.’s (2006) most robust effects were observed for college degree completion, we did not have an index of degree completed and instead used a cutoff based on years of education completed (our cutoff of less than 16 years was designed to be parallel to a bachelor’s degree, but we have no indication whether the degree was obtained). For substance use, we analyzed binary measures of use and dependence whereas King et al. used growth models to create continuous slope and intercept measures for consumption. In addition, their drug use measure was a composite of eight illicit drugs; our drug use analyses focused on cannabis, although we did include a measure of any illicit drug dependence (which was not significant in
