The DID Model The causal effect in natural experiment: TATT E[YiYox I D:=1]=E[Y D:=1]-E[Yor D:=1] Counterfactual result. How to estimate E[Yoz I Di=1]? 6
• The causal effect in natural experiment: • Counterfactual result. • How to estimate ? 6 The DID Model
The DID Model The model specification: 因果效应 VD】 yDel Yoo T=0 T-1 7
• The model specification: 7 The DID Model
The DID Model The model specification Yi=a+BD;+8T+r(DiX T) E[Y。|D:,T]=a十D,+T+r(DXT) EYg{D:=0,T=0]=a E[Ym1D,=0,T=1]=a+8 E[Ya|D,=1,T=0]=a+3 E[Y.ID:=1,T=1]=a+B+8+t
• The model specification : 8 The DID Model
The DID Model The model specification x={E[Y。ID=1,T=1]-E[YgID,=1,T=0]} -{E[Y。1D:=0,T=1]-E[Y。|D=0,T=0]} ·If we control for X Ya=a+8D;+8T+r(D:X T)+X3Y ·Why we control for X? Natural experiment and quasi-natural experiment. 9
• The model specification : • If we control for X: • Why we control for X? • Natural experiment and quasi-natural experiment. 9 The DID Model