This application proposes to develop three key components in person-centered longitudinal statistical models: (a) a comprehensive simulation study designed to understand the nuanced performance of a wide range of models used to derive group based trajectories, (b) a cross-validation procedure designed to bolster the confidence (in terms of replication and consistency) of these models when employed in controlled, clinical trials and effectiveness trials, and (c) to promote dissemination of these advanced techniques by developing a user- friendly, freely available software with a graphical-user interface.