Control Variable 。When we control for X: X D D (a (b) D 11
• When we control for X: 11 Control Variable
Control Variable The problem for control variables in OLS: A represents a set of omitted variables: Y=a+ps;+Ay+8 Cov(YSD=p+r8s V(S,) .6 Is the coefficient for 4 in a regression of S on 4. 12
• The problem for control variables in OLS: • A represents a set of omitted variables: • 𝛿 Is the coefficient for A in a regression of S on A. 12 Control Variable