Fig. 1

Final GMM solution. a The estimated proportion of class membership was 73% for class 1 and 27% for class 2. The slope and quadratic terms were significant for class 1, but not for class 2 (see Additional file 1: Table S2 for parameter estimates). The trajectories observed by Szatmari et al. [30], by modal class assignment, are superimposed with dotted lines. b Observed ABC scores by most likely class assignment