2.3.Classification of Forecasts -Objective Causal Model We may choose a and b to minimize(y(+ by letting 0g =0 Ba →22[y-(a+bx】-0a=2y-bx]=-饭 n i=1 .- 6 =0 →2[y-a+x小()-0 →b=L i=1 x-x∑x i=1 i=1Causal Model 2 1 ( , ) [ ( )] n i i i g a b y a bx  We may choose a and b to minimize    by letting 0 g a      1 2 0         n i i i y a bx    1 0         n i ii i 0 y a bx x gb   2.3. Classification of Forecasts - Objective 1 1 2 1 1             n n ii i i i n n i i i i x yyx b x x x   1 1      n i i i a y bx y bx n