Proof that Instrumental Variables estimators are Two Stage Least Squares

[@rodolfo1654]

Hello Ben! Thank you for showing this beautiful proof! I was wondering what it would look like if we added a covariate to both stages (e.g. eta*Wi where eta is the coefficient and Wi a control variable). Would the proof hold? Thank you!😃

[@henriqueramos6947]

Hi, Ben. First of all: congrats for your excellent videos. They have been very useful to me. One question: Wouldn't be Cov(X_hat,X) instead of Var(X_hat) when you indicate the B_2SLS ? The conclusions doesn't alter at all, but the calculations gets simplier.