This proposal requests funding for the Prevention Science and Methodology Group (PSMG) to continue its development of designs and analyses for preventive trials in mental health. These methodologic advances are fundamental to improving the science of prevention both at the National Institute of Mental Health and at the National Institute of Drug Abuse. Centered at the University of South Florida and at UCLA, PSMG includes methodologic collaborators at the Oregon Social Learning Center and Johns Hopkins, and collaborates with prevention centers conducting trials to prevent mental disorders as well as delay the onset and abuse of drugs. We propose developing extensions to developmental trajectory or growth modeling that have direct relevance to prevention, including (1) modeling interactions between intervention condition and each individual's baseline score to examine variation in an intervention's impact on proximal and distal targets, (2) mixture modeling to examine heterogeneity in developmental pathways and how these pathways change as a function of intervention, and (3) examining contextual effects on multiple dimensions of growth. A second aim is to extend methods for assessing the effect of variation in both program implementation and subjects' level of participation. Such methods are needed to move from efficacy to effectiveness studies. We will also develop new methods for handling missing data, particularly involving selection bias and attrition. The third aim involves the scientific design of randomized preventive trials. These methododologic developments will be applied to ongoing preventive trials at Johns Hopkins and the Oregon Social Learning Center.