We used LD score regression to estimate the SNP‐based heritability of the six EEG phenotypes following the recommendations in Bulik‐Sullivan et al. (2015b), including pruning for Hapmap 3 SNPs. Next, the LD‐score regression intercept was used to assess quality of the GWAS and removal of stratification effects by the population Principal Components (see for example Okbay et al., 2016a). Finally, we used bivariate LD‐score regression to estimate genetic correlation rG, between the EEG phenotypes and GWASs available in LD Hub (http://ldsc.broadinstitute.org) (Bulik‐Sullivan et al., 2015a; Zheng et al., 2017). This includes GWASs on schizophrenia and alcohol use disorders. We additionally examined bipolar disorder, subjective wellbeing, neuroticism, generalized epilepsy and educational attainment (ILAE Consortium, 2014; Okbay et al., 2016b), to explore the genetic association of oscillatory activity with these behavioral and neurological traits. Finally, we investigated genetic correlations between our EEG GWAS results and the ENIGMA GWAS results for subcortical volumes, intracranial volume, and brain volume. See Supporting Information Methods for a full reference list.
