“…Volatility forecasts play an important role in risk management, asset pricing, and portfolios, and methods of improving the accuracy of volatility prediction represent an important and difficult issue (see, e.g., Ji and Guo, 2015 ; Rossi and Fantazzini, 2015 ; Wang et al, 2016 ; Degiannakis and Filis, 2017 ; Ma et al, 2017 ; Wang et al, 2018a ; Ma et al, 2019 ; Zhang et al, 2019b ; Bai et al, 2020 ; Liang et al, 2020a ; Liang et al, 2020b ; Wei et al, 2020 ; Zhang et al, 2020 ; Liang et al, 2021 ). In addition, numerous studies have examined the factors that affect oil prices (see, e.g., Elder et al, 2013 ; Zhang and Cao, 2013 ; Sévi, 2014 ; Wang et al, 2016 ; Zhang, 2017 ; Jing et al, 2018 ; Wang et al, 2018b ; Zhang et al, 2019a ).…”