4If explanatory variables appear in the GJR equation, ω is then replaced by σ2[     (          )       ]
 1- ∑q αi- γiE(St-) - p∑ βj
    i=1              j=1- i=1n2ωixi, where xi is the sample average of variable xi,t (assuming the stationarity of the n2 explanatory variables).