My research combines statistical and substantive work, with a developmental perspective. Broadly, my statistical interests include latent variable models, psychometrics and the analysis of change. Recently, my focus has been on the use of latent class and mixture models, especially model selection and as psychometric models. Substantively, my work focuses on cigarette smoking & nicotine dependence; substance use in general; and adolescent development. My recent substantive work has focused on the identification and measurement of cigarette smoking and substance profiles or patterns.