Variance(方差) Variance=E[(X-E(X)2]=E[X2]-[E(X)]2= Standard deviation(标准差)OX Coefficient of variation 1(变异系数) 6= E(x) Lxl Variance (方差) Variance= Standard deviation(标准差) Coefficient of variation (变异系数) 2 2 2 2 [( ( ) ] [ ] [ ( )] E X E X E X E X X X X X X E x ( )