2.3.Classification of Forecasts-Objective Causal Model g(a,b)=∑y-(a+bx i=l og=0 a=y-bx Ba ag =0 ∑xy-∑xn∑xy-∑x ab b=i i=l i=1 i=1 x-x2x2x-2x i= i=1 i=1 S,=2y-2%:S=2x- 之x:-∑%Causal Model 2 1 ( , ) [ ( )] n i i i g a b y a bx     0 g a    a  y  bx 1 11 1 2 2 11 1 1 n nn n ii i ii i i ii i xy nn n n xx ii i i ii i i x y y x n x y ny x S b S x x x n x nx x                   0 g b    2 2 ; () n nn n n xy i i i i xx i i i ii i i S n xy x y S n x x        1 1 ; ; n n i i i i x xy y n n     2.3. Classification of Forecasts - Objective