Pantos, T., S. Polyzos, A. Armenatzoglou, and I. Kampouris. “Volatility Spillovers in Electricity Markets: Evidence from the United States”. International Journal of Energy Economics and Policy, vol. 9, no. 4, June 2019, pp. 131-43, https://www.econjournals.com/index.php/ijeep/article/view/7563.