Competing models were compared visually using mean and individual trajectory plots, BIC and AIC fit indices, and chi-square difference tests (when available for nested models). Based on these criteria, the optimal functional form retained for mother- and adolescent-reported scores was a one-piece linear model and for father-reported scores was a two-piece linear model.3 For fathers, the two-piece model delineated change from ages 2 to 7 and 7 to 17 through two linear slope parameters, best reflecting the pattern of change evident in our data. In unconditional trajectory models for each sub-sample, parameter estimates indicated significant, steady decreases in externalizing symptoms from ages 2 through 17 in mother-reported scores, steeper declines in externalizing for ages 2 through 7 than for ages 7 through 17 in father-reported scores, and steady increases over ages 10 through 17 in adolescent-reported scores (see Hussong, Wirth et al., 2007 for details).
