“…To understand and better illustrate the effect of potential variables on the performance of the ARH model, we further consider the extensions of the AR and ARH models, which include potential variables. We use 12 macroeconomic variables (see, e.g., Christiansen et al, 2012; Rapach et al, 2010; Welch & Goyal, 2008; Zhu & Zhu, 2013), three uncertainty variables (see, e.g., Jurado et al, 2015; Ludvigson et al, 2015), oil volatility (Wang et al, 2018), geopolitical risk uncertainty (GPR) (Mei et al, 2020), and economic policy uncertainty (EPU) (see, e.g., Christou et al, 2018; Li et al, 2020; Ma et al, 2020) as potential variables to check robustness. With positive values obtained for each of the additional variables, our results are robust to the addition of these potential variables.…”