Given the large number of observations available, it became possible to estimate mean rates of change of development with considerable accuracy. This enabled the identification of striking sex differences in age-specific developmental patterns and the effects of genotype on development with a similar range of effect sizes as found in comparable GWA studies. Preliminary studies of other P3 related phenotypes derived from the same subjects with the same methodology show similar patterns of sex differences in mean rates of change but manifest different patterns of genotypic effect. This suggests that relatively large neurophysiological systems governed by multiple genetic factors may experience coordinated developmental patterns regulated by sex specific effects. A more comprehensive multivariate description of the genetic architecture of the P3 response can be obtained using EROs from different frequency bands and experimental conditions and using a number of different measures of the response, together with a number of different genetic factors known to affect neurophysiological and neuroanatomical features. Since measures of the P3 response have been found to be useful endophenotypes for the study of substance abuse disorders (Euser
