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st: RE: mahapick updates


From   "Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: mahapick updates
Date   Thu, 17 Apr 2008 08:55:39 -0700

We'll need to do it on Monday.  I don't like to give special exams
before the main exam.

Tony

Peter A. Lachenbruch
Department of Public Health
Oregon State University
Corvallis, OR 97330
Phone: 541-737-3832
FAX: 541-737-4001

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of David Kantor
Sent: Thursday, April 03, 2008 8:53 AM
To: Statalist
Subject: st: mahapick updates

Thanks to Kit Baum, updates to the mahapick package are now available on
SSC.

The mahapick package has programs to calculate a distance measure 
(propensity score, dissimilarity measure) between observations, and 
to choose a set of close matches for a selected subset of observations.

There are two important changes:

1, this now implements a true Mahalanobis distance measure -- whereas 
previously, it was the normalized Euclidean distance. The true 
Mahalanobis measure accounts for correlation between variables. (The 
old behavior is available as an option.)

2, the new program mahascores enables you to directly obtain the 
distance measures between all pairs of observations. The concept of 
"treated" observations is optional. And, while there is some overlap 
with some of the functionality of mahapick, this would be the 
preferred method if all you want is the distance measure (and don't 
need, at this stage, to select the closest matches).  The results can 
be placed into the current dataset, a separate dataset, or a matrix.

There are other enhancements that should give users more control.

Thanks also go to Heiko Giebler of Wissenschaftszentrum Berlin fur 
Sozialforschung gGmbH -- for the suggestions and advice that led to 
these improvements.

To download...
ssc desc mahapick
ssc inst mahapick

If any users try it and have any problems, comments, or suggestions, 
I'd like to hear them.
Best wishes,
--David Kantor

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