My quantitative research interests focus on three specific areas: 1) psychometric theory, particularly the strengths and weaknesses of classical true-score theory for the measurement and assessment of individual differences; 2) The design and analysis of controlled clinical trials, and the use of the generalized linear mixed model in the analysis of such designs; and, 3) 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. 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 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 the development of broader-based prevention programs that attempt to cast a larger net); and, 3) 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.