112出现异方差性时的OLS 估计 var(B,)= ∑ 2 var(B2) ∑x2 2021/220 Hongfeng Peng Department of Finance, wuhan Univers ity2021/2/20 Hongfeng Peng Department of Finance, Wuhan University 5 11.2 出现异方差性时的OLS 估计 2 2 2 2 2 ˆ var( ) ( ) i i i x x   =   2 2 2 ˆ var( ) i x   = 