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st: -psmatch2- query


From   "Stephen P. Jenkins" <stephenj@essex.ac.uk>
To   Edwin Leuven <e.leuven@uva.nl>
Subject   st: -psmatch2- query
Date   Thu, 27 Mar 2003 17:44:58 +0000 (GMT Standard Time)

Dear Edwin,

I've just started using your and Barbara's -psmatch2-.  Unfortunately I 
seem to have hit an error running the program that is inexplicable to 
me: see below.  I am a novice at the matching game, so may have 
committed some basic mistake -- in which case tell me. :)  But, if not, 
I'd be interested in your comments and suggestions about the following.

. psmatch2 man age edq* if hhsize == 1 & age > 17 & age < 59

Probit estimates                                  Number of obs   =       4936
                                                  LR chi2(7)      =      79.57
                                                  Prob > chi2     =     0.0000
Log likelihood = -3358.7944                       Pseudo R2       =     0.0117

------------------------------------------------------------------------------
         man |      Coef.   Std. Err.      z    P>|z|     [95% Conf. Interval]
-------------+----------------------------------------------------------------
         age |  -.0127112   .0017197    -7.39   0.000    -.0160818   -.0093406
        edq0 |   .0435198   .1366683     0.32   0.750    -.2243451    .3113846
        edq1 |  -.0652628   .1455057    -0.45   0.654    -.3504488    .2199232
        edq2 |  -.2005075   .1350892    -1.48   0.138    -.4652775    .0642625
        edq3 |  -.0388344   .1352087    -0.29   0.774    -.3038385    .2261697
        edq4 |   .0508258   .1326242     0.38   0.702    -.2091129    .3107644
        edq5 |  -.1211298   .1337885    -0.91   0.365    -.3833505    .1410908
       _cons |   .6478857   .1409365     4.60   0.000     .3716552    .9241163
------------------------------------------------------------------------------
There are control 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.
Matching Method: neighbor, Metric: pscore
_ ambiguous abbreviation
could not restore sort order because variables were dropped
r(111);

. de _*

              storage  display     value
variable name   type   format      label      variable label
-------------------------------------------------------------------------------
_pscore         double %10.0g                 psmatch2: Propensity Score
_treated        float  %22.0g      _treated   psmatch2: Treatment assignment
_weight         double %10.0g                 psmatch2: # Matches per obs.
_n1             float  %9.0g                  psmatch2: ID of nearest neighbor
_id             float  %9.0g                  psmatch2: Identifier (ID)
_pdif           double %10.0g                 psmatch2: abs(pscore -
                                                pscore[nearest neighbor])


-set trace on- shows that the error comes as follows in the program 
code:

 }
- qui replace _treated = -1 if `treat'==0 & _treated==2
- qui replace _weight = . if _treated==2 | _weight==0
- qui replace _`outcome' = . if !inlist(_treated,0,1)
_ ambiguous abbreviation
could not restore sort order because variables were dropped
r(111);

I get the same error regardless of whether the original sort order is 
randomised or not. I also got the same error when using just "age"
rather than "age edq*" in the indepvars list.

TIA

regards
Stephen
----------------------
Professor Stephen P. Jenkins <stephenj@essex.ac.uk>
Institute for Social and Economic Research (ISER)
University of Essex, Colchester, CO4 3SQ, UK
Tel: +44 (0)1206 873374. Fax: +44 (0)1206 873151.
http://www.iser.essex.ac.uk

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