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st: RE: confusion about psmatch2

From   "Nick Cox" <>
To   <>
Subject   st: RE: confusion about psmatch2
Date   Sat, 27 Mar 2004 17:24:09 -0000

There's stuff here I've never heard about. 

Can you explain how OLS can estimate "causal effects" please? 


Lijun Song
> As a beginner at Stata, I am confused about the psmatch2.
> Suppose I am interested in the causal effect of college (a 1-0 
> treatment indicator) on income. I also assume that race, sex, and 
> family background (such as Mother and Father's SEI) will 
> influence the 
> treatment assignment. I also could not deny that race,sex, and family 
> background also influence the outcome of interests, income directly.
> Then, after regressing income on college, I arrive at an estimated 
> coffecient. After that, I use "psmatch2 college race sex masei pasei".
> I think the causal effect estimated by OLS estimator should be higher 
> than those by Propensity Score Matching right?
> But my results show that the causal effect estimated by OLS 
> is smaller 
> than these by Propensity Score Matching. Why?
> In addition, the causal effect estimated by OLS is ATT or ATE?

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