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From |
"Charman, Susan" <scharman@rcseng.ac.uk> |

To |
<statalist@hsphsun2.harvard.edu> |

Subject |
st: propensity score matching |

Date |
Thu, 8 May 2008 20:51:23 +0100 |

Dear Stata users I would welcome some advice on the use of psmatch2 - I seem to have become confused somewhere along the line. I have estimated a propensity score using logistic regression. I now want to match on this and then use conditional logistic regression to assess the effect of treatment on outcome. I have approximately 11000 subjects on treatment A and 2300 on treatment B. I was hoping to create a matched data set with A:B in the ratio n:1 where 1<n<4. I had hoped that psmatch2 would do this with nearest neighbour matching without replacement. However I seem to be having some problems or am misunderstanding the help. 1. I was under the impression that "standard" nearest neighbour matching is done without replacement (matches removed) and yet psmatch2 creates the _weight for which I get very high values ( e.g n=45) . this suggests that a subject is used 45 times as a match ( there are other subjects available with the same propensity score but not used). 2. I would like to do 4:1 matching but cannot seem to find a way of identifying the id's of all the matches - is this possible. If not can I get the outcomes for all the matched pairs so that I can compute OR's. Many thanks Susan * * For searches and help try: * http://www.stata.com/support/faqs/res/findit.html * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**Re: st: propensity score matching***From:*Steven Samuels <sjhsamuels@earthlink.net>

**Re: st: propensity score matching***From:*David Kantor <kantor.d@att.net>

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