For subsequent analyses, we created composite endophenotype measures. For those measures recorded from one primary scalp area (P3 amplitude and TF-PC1 peak energy, which were recorded from three closely spaced parietal electrodes) we averaged across the three electrode sites. For beta, we created a composite consisting of the first principal component of the covariance matrix of the three electrodes. Loadings for the bipolar occipital leads were approximately twice as great as the loading for the monopolar Cz recording. The scree plot clearly indicated that one component, which accounted for 78% of the variance, was warranted for beta.
