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st: Pmatch2 and random


From   "Gauri Khanna" <[email protected]>
To   [email protected]
Subject   st: Pmatch2 and random
Date   Fri, 13 Apr 2007 09:26:48 +0000

Dear Stata list,

I am running the psmtach2 command to estimate propensity scores. I use Stata 9.2 and psmatch2 is updated.

While running this command, in my output I get a comment:

"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"

So I do the following
-gen random=uniform()
sort random-

but still get the same message, I also try with -set seed- as below but get the same message.

-set seed 12345
-gen random=uniform()
sort random-

I copy below my command and output. Does anyone know how to correct this problem?
.
. psmatch2 waterpipe sexhhead v152 v012 ageresp2 aware ///

v512 v715 eduhusb v730 partnerage2 v025 housetype2 ///
sh42 ownerTV hv211 sh47q, out(h11) n(5) logit
Logistic regression Number of obs = 24869
LR chi2(16) = 6171.00
Prob > chi2 = 0.0000
Log likelihood = -13440.218 Pseudo R2 = 0.1867

------------------------------------------------------------------------------
waterpipe | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
sexhhead | .081646 .0614635 1.33 0.184 -.0388202 .2021123
v152 | -.0036941 .0010471 -3.53 0.000 -.0057463 -.001642
v012 | .0361599 .0220871 1.64 0.102 -.00713 .0794498
ageresp2 | .0001226 .0003905 0.31 0.754 -.0006428 .000888
aware | .51381 .0374203 13.73 0.000 .4404675 .5871525
v512 | -.066041 .005295 -12.47 0.000 -.076419 -.055663
v715 | .0116712 .0090949 1.28 0.199 -.0061545 .029497
eduhusb | -.0002637 .0006224 -0.42 0.672 -.0014835 .0009562
v730 | .0377528 .0103074 3.66 0.000 .0175506 .057955
partnerage2 | -.0004689 .0001196 -3.92 0.000 -.0007032 -.0002346
v025 | -1.486734 .0365479 -40.68 0.000 -1.558367 -1.415102
housetype2 | -.0481205 .0312731 -1.54 0.124 -.1094148 .0131737
sh42 | -.2851831 .0532543 -5.36 0.000 -.3895597 -.1808065
ownerTV | .5799184 .0394479 14.70 0.000 .5026019 .657235
hv211 | .2489998 .0539778 4.61 0.000 .1432052 .3547944
sh47q | -.7165624 .0595988 -12.02 0.000 -.8333739 -.5997508
_cons | .6628973 .3185432 2.08 0.037 .0385641 1.28723
------------------------------------------------------------------------------
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.
----------------------------------------------------------------------------------------
Variable Sample | Treated Controls Difference S.E. T-stat
----------------------------+-----------------------------------------------------------
h11 Unmatched | .414652169 .389711613 .024940556 .01043801 2.39
ATT | .414652169 .365248601 .049403568 .014874442 3.32
----------------------------+-----------------------------------------------------------
Note: S.E. for ATT does not take into account that the propensity score is estimated.

| psmatch2:
psmatch2: | Common
Treatment | support
assignment | On suppor | Total
-----------+-----------+----------
Untreated | 15,396 | 15,396
Treated | 9,473 | 9,473
-----------+-----------+----------
Total | 24,869 | 24,869

Sincerely,

Gauri

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