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From |
"Gao Liu" <gao.liu@gmail.com> |

To |
statalist@hsphsun2.harvard.edu |

Subject |
Re: st: One to N matching |

Date |
Tue, 18 Nov 2008 14:11:49 -0500 |

Thanks, Rich, Maybe i did not make a clear enough description of my question. vmatch can match all observations based on certain criteria, like within some distance. However, what I want is the nearest N observations, where n is a fixed number. Also, duplicates are not allowed. Best Gao On Tue, Nov 18, 2008 at 1:24 PM, Richard Goldstein <richgold@ix.netcom.com> wrote: > -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 >>> >>> * >>> * For searches and help try: >>> * http://www.stata.com/help.cgi?search >>> * http://www.stata.com/support/statalist/faq >>> * http://www.ats.ucla.edu/stat/stata/ >>> >> * >> * For searches and help try: >> * http://www.stata.com/help.cgi?search >> * http://www.stata.com/support/statalist/faq >> * http://www.ats.ucla.edu/stat/stata/ >> >> > * > * For searches and help try: > * http://www.stata.com/help.cgi?search > * http://www.stata.com/support/statalist/faq > * http://www.ats.ucla.edu/stat/stata/ > * * For searches and help try: * http://www.stata.com/help.cgi?search * http://www.stata.com/support/statalist/faq * http://www.ats.ucla.edu/stat/stata/

**Follow-Ups**:**RE: st: One to N matching***From:*"Nick Cox" <n.j.cox@durham.ac.uk>

**References**:**st: One to N matching***From:*"Gao Liu" <gao.liu@gmail.com>

**Re: st: One to N matching***From:*Richard Goldstein <richgold@ix.netcom.com>

**Re: st: One to N matching***From:*"Austin Nichols" <austinnichols@gmail.com>

**Re: st: One to N matching***From:*"Gao Liu" <gao.liu@gmail.com>

**Re: st: One to N matching***From:*Richard Goldstein <richgold@ix.netcom.com>

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