Extending a previous study of the development of theta band EROs (Chorlian et al., 2015) and as used in Chorlian et al. (2017), the model includes a genotypic value and a sex × genotype interaction, consistent with other studies of human development (Widén et al., 2010; Cousminer et al., 2013). Weights for individuals in the local linear regression model were adjusted to account for multiple observations on single individuals and co-presence of sibs in each of the regression calculations. The bandwidth for the kernel (Epanechnikov) was taken as 0.6 to minimize the mean squared error, although the variation in the size of the error was less than 2% over the range of bandwidths from 0.4 to 0.8.
