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Re: st: One to N matching


From   Richard Goldstein <richgold@ix.netcom.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: One to N matching
Date   Tue, 18 Nov 2008 13:24:58 -0500

-vmatch- does provide 1 to N because it finds all matches for each case; in a recent match that I did I found anywhere from 1 to 18 matches for each of my cases

Rich

Gao Liu wrote:
Thank you, Richard and Autstin,

The score in my dataset is actually from psmatch2. Although psmatch2
provides 1 to n matching, but it does not indicate which non-case
observations are matched to the case obs, except for the nearest one.
Also it allows duplicated matching. That is why I plan to do it by
hand.

I just checked the command, vmatch. I did not find that it provdes the
option of 1 to N matching.

Austin, can you decribe some more how to do it by hand.

best

Gao

On Tue, Nov 18, 2008 at 11:32 AM, Austin Nichols
<austinnichols@gmail.com> wrote:
Gao Liu--
Actually, I think you are looking for -psmatch2- (findit psmatch2).
Or did you want to program the matching by hand?  That is also
possible, and not very hard in the case where all you want is the
nearest N matches.  However, note that the order of matching will
matter in the situation you describe--matching without replacement--so
you should probably do the matching many times and compute statistics
using the rules of variance computation for multiple imputation.

On Tue, Nov 18, 2008 at 11:07 AM, Richard Goldstein
<richgold@ix.netcom.com> wrote:
for already existing programs, rather than writing your own, I would start
with -vmatch- (user-written, type -findit vmatch-)

I'm not sure it will cover your last criterion (used only once) but if not
it should be easy to eliminate those

Rich

Gao Liu wrote:
Dear Statlist:

I have a question about one to N matching.

I have a dataset containing three variables: id, score, case, where
case is a dummy variable indicating whether or not the observation is
in the case group. How can I match each case observation to N non-case
observation based on the score?  Each case observation matches to the
N non-case observations with the closest scores, but no case
observation can match the same observation (i.e. the non-case
observation can be used only one time).

Thank you

Best

Gao
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