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Re: st: One to N matching


From   "Gao Liu" <gao.liu@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: One to N matching
Date   Tue, 18 Nov 2008 13:04:41 -0500

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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