Comparison of height acceleration curves in the Fels, Zurich, and Berkeley growth data.

A new type of smoothing spline designed for nonparametric estimation of growth acceleration curves was applied to longitudinal measures of height from the Fels, Zurich, and Berkeley growth studies. Landmark features of the individual acceleration curves were located and examined for site effects and site by sex interaction. The curves in each group were structurally averaged by transforming the age scale of each child to align the landmarks with overall means. The modal shapes of the structural average curves were found to be highly similar in the three studies, although the relative number of children who conformed to the modal pattern differed among the studies. Significant site by sex interactions were found in the timing of the landmarks associated with the pubertal growth spurt and with the prepubertal 'midspurt'.