To model growth curves of externalizing problems from ages 5–27, we used the lme function of the nlme package (Pinheiro, Bates, DebRoy, & Sarkar, 2009) in R 3.0 (R Development Core Team, 2009) for hierarchical linear modeling (HLM). Because our aim was to predict risk for externalizing problems in adulthood, we set the intercept at age 27 rather than at age 5, consistent with other studies investigating externalizing trajectories (e.g., Owens & Shaw, 2003). Various curvilinear forms of growth were compared. After settling on a form of growth, we related the risk factors individually to the growth curves and then collectively (similar to the approach by Owens & Shaw, 2003), taking a best predictors approach.
