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st: psmatch2 and the options ATE and COM


From   Sarah Wichmann <wichmann.sarah@googlemail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: psmatch2 and the options ATE and COM
Date   Tue, 10 Mar 2009 11:50:54 +0100

Hello,
I am working with Propensity Score Matching and came across the
following problems (code below).

1) When comparing the results from psmatch2 with pscore (and
subsequently att*), I only get the same results if I do not use the
common support options. If I do that, the results differ. I guess the
common support is selected differently with the two commands, but I
could not find more information. Can somebody explain the difference?

2)  When I use psmatch2 again with the common support option, I get
different results for ATT depending on if I also use the ATE option or
not. As I understood the help file, the ATE option should only add
further details in the output instead of changing the calculation,
therefore I do not understand the changing result.

Thanks for your time and consideration,
Sarah


psmatch2 emsbinary logvossd, radius cal(0.1) out(perfbinary) logit com ate

Variable     Sample |    Treated     Controls   Difference         S.E.   T-stat
----------------------------+-----------------------------------------------------------
      perfbinary  Unmatched |       .625   .582417582   .042582418
.045186234     0.94
                        ATT | .612903226   .620169943  -.007266717
.048401842    -0.15
                        ATU | .581497797    .55933642  -.022161378
                        ATE |                          -.018370454


psmatch2 emsbinary logvossd, radius cal(0.1) out(perfbinary) logit com

Variable     Sample |    Treated     Controls   Difference         S.E.   T-stat
----------------------------+-----------------------------------------------------------
      perfbinary  Unmatched |       .625   .582417582   .042582418
.045186234     0.94
                        ATT | .612903226   .620364171  -.007460945
.048395422    -0.15


attr perfbinary emsbinary logvossd, pscore(pscore) logit comsup

n. treat.   n. contr.         ATT   Std. Err.           t
---------------------------------------------------------

      159         454       0.027       0.046       0.580





-- 
Sarah Wichmann
Eichelhäherkamp 94b
22397 Hamburg

Handy: 0046 73 683 57 91
           0049 173 612 44 42

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