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st: propensity score, psmatch2, question

From   Aakanksha Pande <>
Subject   st: propensity score, psmatch2, question
Date   Thu, 8 Dec 2011 11:42:37 -0500

I am using psmatch2, perform Mahalanobian matching with calipers
defined by .25* std dev of propensity score and would appreciate
clarification on the following three questions, for which I am having
a hard time finding answers to on the stata archive, online, or in any

My code is:

set seed 1234
generate x= uniform()
sort x
label variable x "Random variable"

bs, reps(1000): psmatch2 treatment,  ///
out(y) ///
 mahalanobis(x1 x2 x3 x4) ///
 caliper (.11116)

My unanswered questions are on:
1.Does this code do Mahalanobian matching with replacement? If so, does
psmatch2 adjust for the number of times the control observation is used as
a match for different treatments? If not, how does one do so.
2. Is the matching based on Mahanalobian distance a one to one or many to
one match? If many to one, does psmatch2 appropriately weight for number of
3. Bootstrap: Can I use these bootstrap standard errors even though they
are not based on a kernel estimator as suggested by Abadie and Imbens?

Thank you for your help!
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