A discrete time survival analysis (DTSA) using Mplus Version 7.4 (Muthén & Muthén, 1998–2013) was performed to explore longitudinal risk of marijuana initial use (Muthén & Masyn, 2005). Discrete time survival analysis is a specific type of survival analysis that models the timing of events, specifically when events are measured in discrete-time or grouped-time intervals (Masyn, 2014). This model specification allows for the inclusion of time-varying and time-invariant predictors. The event of interest for this particular analysis is defined for each participant as marijuana use initiation, and the survival time is defined as the time elapsed from age to the first marijuana use. The time scale was recorded in discrete-time intervals – age – so although the time-to-event process may actually be more continuous in nature, the data limitations required the process be modeled using DTSA. Fall of first grade aggression and the population stratification variable were grand mean centered to ease in the interpretation of the interaction. In order to explore the moderation of one covariate effect by another, an interaction term is included as a predictor in the
