Table 1 gives family correlations produced by RFGLS for P3 amplitude and phenotypic factor scores from the common pathway model, which was the basis for estimating genetic factor scores. The pattern of correlations suggests substantial genetic influence and little shared environmental influence. This was confirmed by the results of biometric model-fitting analyses, summarized in Table 2. Heritability estimates for both endophenotypes (P3 amplitude and the P3 common factor) were substantial, indicating that between half and nearly two thirds of the variance in them was due to additive genetic influence. Heritability estimates were somewhat larger in magnitude for the common factor. Point estimates of C were nonzero in estimates obtained from twin data, although the confidence interval included 0. This indicated that shared environment is likely not a significant influence.
