My quantitative research interests focus on three specific areas; 1) The design and analysis of randomized controlled trials, and the use of the generalized linear mixed model and its extensions in the analysis of such designs; 2) latent variable modeling, and in particular, the utility and limitations of latent variable growth curve and latent class growth mixture models in the assessment of change over time; and,3) psychometric theory, particularly the strengths and weaknesses of classical true-score theory for the measurement and assessment of individual differences; My interests in substance abuse have focused on: 1) the etiology of such abuse, particularly those individual, familial, and social factors that place an individual at increased risk for the development of a drug-abusing lifestyle; 2) the development of conceptual models that explain responsiveness to drug-abuse treatment for drug-abusing individuals, where such models utilize the results of baseline assessment information to explain differential responsiveness to treatment; and 3) the development of conceptually-based prevention programs that seek to impact at-risk individuals, where such programs are based on information about the risk factors of the individuals involved, that is, prevention and intervention programs that are directed by the risk-factor information available from the participants (rather than on universal prevention programs).