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AW: st: PSMATCH with 2 conditions


From   "Mihai-Andrei Popescu-Greaca" <mischai@gmx.de>
To   <statalist@hsphsun2.harvard.edu>
Subject   AW: st: PSMATCH with 2 conditions
Date   Mon, 20 Sep 2010 00:55:46 +0200

Hi Judson,

thanks for the great tip & sorry for the late reply but I've been pretty
busy lately.

One thing though:
My industry is only 2 digit, so if I only want to match by industry, I just
multiply industry by 10 and then add the pscore, as follows:
gen pscore2=3-digit-industry*10+pscore
And then psmatch2 as indicated by you in the link.
THE PROBLEM occurred when I used 1000 instead of 10, and then 100000 instead
of 1000; ALL 3 yielded different results (T & Z-scores when bootstrapping
SEs)

Do you have an explanation for the different results??

Regards,
Mihai 

-----Ursprüngliche Nachricht-----
Von: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] Im Auftrag von Caskey, Judson
Gesendet: Dienstag, 7. September 2010 20:08
An: statalist@hsphsun2.harvard.edu
Betreff: re: st: PSMATCH with 2 conditions

See the following post for an example of forcing a match:

http://www.stata.com/statalist/archive/2010-09/msg00073.html

In your case, say you have a 4-digit industry code (e.g. SIC). You can first
compute propensity scores, then make a new variable pscore2 that looks like:

pscore2 = year*100000+industry*10+pscore

If you have year 1999, industry 1234 and p-score 0.25, you get:

pscore2 = 199912340.25

If you put a caliper of, say, 0.5, it is impossible to match to a firm in a
different industry/year.

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