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st: How to extract matched sample in psmatch2


From   "Wald,Kenneth D" <kenwald@ufl.edu>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: How to extract matched sample in psmatch2
Date   Sun, 30 Oct 2011 21:02:58 +0000

I'm using psmatch2 to generate a comparison sample of one group of survey respondents with another, defined by religious affiliation. I've run a basic analysis but can't figure out how the program gets to the next step--creating the matched sample so I can confirm that the covariates are indeed balanced. For the moment, I don't want to run multivariate analysis or use weighting. I just want examine the values of certain other variables in the two groups, the base and the matched subsample. I've read the documentation and Guo and Fraser but nothing walks me through the program. So I'd be grateful if somebody could recommend something that really explains the Stata routine to do that. 

Here's the commands I've used and the output. The program generates pscores (_pscore). I did randomize the order of cases prior to estimating the equation as advised. Two other questions if you're inclined. With a dichotomous grouping variable, why did Stata use probit instead of logit which I thought was the default. And, given the distinctive geographical distribution of the base group, I used two location variables--state and region. They are nominal variables and so don't really belong in this kind of model. (I also need the year variable so the sample is balanced on that as well.)

Thanks.

psmatch2 jewish citysize nielsen employ year race3 region9 sex state agematch faminc educ3, caliper(11.8)

Probit regression                                 Number of obs   =      91143
                                                  LR chi2(11)     =    3863.45
                                                  Prob > chi2     =     0.0000
Log likelihood =  -8533.966                       Pseudo R2       =     0.1846

------------------------------------------------------------------------------
      jewish |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
    citysize |   .1399825   .0074226    18.86   0.000     .1254345    .1545305
     nielsen |     .26099    .023412    11.15   0.000     .2151035    .3068766
      employ |  -.0502017   .0233954    -2.15   0.032    -.0960559   -.0043475
        year |  -.0005044   .0023767    -0.21   0.832    -.0051626    .0041538
       race3 |   1.132129    .069947    16.19   0.000     .9950352    1.269222
     region9 |  -.0962822   .0044346   -21.71   0.000    -.1049738   -.0875906
         sex |   .0162921   .0209977     0.78   0.438    -.0248626    .0574468
       state |  -.0041037    .000857    -4.79   0.000    -.0057833    -.002424
    agematch |   .0741419   .0133769     5.54   0.000     .0479236    .1003602
      faminc |   .0929483   .0111876     8.31   0.000      .071021    .1148755
       educ3 |   .3533498   .0197301    17.91   0.000     .3146796      .39202
       _cons |  -4.425644   4.717873    -0.94   0.348     -13.6725    4.821217
------------------------------------------------------------------------------
There are observations with identical propensity score values.
The sort order of the data could affect your results.
Make sure that the sort order is random before calling psmatch2.

Kenneth D. Wald
Distinguished Professor of Political Science
University of Florida
POB 117325
Gainesville, FL 32611-7325
Office Phone: 352-273-2391
Email: kenwald@ufl.edu
Home page: www.clas.ufl.edu/users/kenwald

Fall 2011 Semester:
Frankel Center for Advanced Judaic Studies
2111 Thayer Bldg.
University of Michigan
202 S. Thayer Street
Ann Arbor, MI 48104-1608
Department Phone: 734-615-5097
Department Fax: 734-963-2186
Office Phone: 734-615-8541




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