His main areas of interest in quantitative methods are statistical mediation analysis, longitudinal data, and nonlinear models. The motivation for advancing these methods is to improve the development, evaluation and overall efficacy of these interventions, especially those related to substance use. Fritz is an investigator on grants from the National Institutes on Drug Abuse, Estimating Mediation Effects in Prevention Research, and the National Institutes of Health, Reaching and Motivating Change in Teen Marijuana Smokers.