Gender differences in P300 development were most apparent as a divergence of group proportions. Male subjects were consistently more prevalent than female subjects in the low-level P300 groups identified by the trajectory models, especially for the 8–12 year old group where 66% of male subjects but only 33% of female subjects were in the low-level P300 group. As may be seen in Figures 1 and 2, the male and female 8–12 year old trajectory groups show linearly increasing P300 amplitude. The rate of increase was lower in the P300 group having the lowest P300 compared to those in the higher level P300 group (p = 0.045). The 13–18 and 19–29 trajectory groups exhibit a mix of stable and slightly declining P300 patterns from age 13 through age 29.
