These findings may not generalize to studies of P300 at different ages or across a wider number of measurements. Examination of growth curves in past studies of visual P300 amplitude change suggested that a linear model is reasonable for the three time points examined here, and unless it is of a fairly large effect size, a quadratic term would be difficult to detect with three time points. A quadratic component of change was supported by Hill et al. (1999) using the same task as we did but with a wider and largely earlier age range (7–18 years) measured on up to five occasions. Nonlinear influences on P300 change may be important across a broader range of ages than was assessed here, and quadratic change in particular may differentiate at-risk groups. Whether such effects exist for MTFS participants will become clear as subsequent assessments are completed in this longitudinal investigation.
