Z,=(YX)一Y0=XTΠ+E OLS =X(XX)X 估计 之，=(X) OLS估计 △，=(22，)2X =立，△，e=-Z (Y X ) i i i = 0 0 Y0 X 0 0 i i i =  +    Y0 X 0 X(X X) X Y 1 0 i i i = =   −  ( )   Zi Y X i i = 0 0  (   )   i = i i i Yi   − Z Z Z 1     Yi = Zi i e y y il = il − il   OLS 估计 OLS估计