The initial phase of the analysis provides the means, variances, covariances, and correlations of the coherence values of the data set. Although seven frequency bands were available for analysis, only high alpha was analyzed based on its major occurrence in resting state EEG and its use in our previous work (Meyers et al., 2019, 2021). Values at 96 age centers from ages 12 to 31 for each sex were calculated by a local linear regression (LOESS) method and and an adaptation of that method to calculate covariances initially described in Chorlian et al. (2015). Briefly, the weights used in the regression calculation were employed in a weighted covariance analysis. The bandwidth for the kernel (Epanechnikov) was taken as 0.6 as in Chorlian et al. (2015). Quartiles of the values of covariance and correlations matrices were also calculated.
