決定係数
R 2 ≡ ∑ i = 1 N ( f i − f ̄ ) 2 ∑ j = 1 N ( y j − y ̄ ) 2 {\displaystyle R^{2}\equiv {\frac {\displaystyle \sum _{i=1}^{N}\left(f_{i}-{\overline {f}}\right)^{2}}{\displaystyle \sum _{j=1}^{N}\left(y_{j}-{\overline {y}}\right)^{2}}}}