You can set the exact= parameter in your call to matchit. That will force an exact match on the value of Stage.
match = matchit(Group ~ Stage + Age + Gender + PS, myData, method="optimal", exact=c(Stage)) Hope this is helpful, Dan Daniel J. Nordlund Washington State Department of Social and Health Services Planning, Performance, and Accountability Research and Data Analysis Division Olympia, WA 98504-5204 > -----Original Message----- > From: r-help-boun...@r-project.org [mailto:r-help-bounces@r- > project.org] On Behalf Of Polwart Calum (COUNTY DURHAM AND DARLINGTON > NHS FOUNDATION TRUST) > Sent: Tuesday, June 19, 2012 4:37 PM > To: r-help@r-project.org > Subject: [R] matchit - can I weight the parameters? > > This may be a really obvious question but I just can't figure out how > to do it. > > I have a small dataset that I am trying to compare to some controls. > It is essential that the controls are matched on Cancer Stage (a > numerical factor between 1 and 4), and then ideally on Age (integer), > Gender (factor), Performance Status(factor). > > I'm using matchit to try and do this, but it seems to give equal > priority to all my variables so I can be relatively well matched on > Age, Sex and PS but not exactly matched on Stage. Stage is the biggest > influence on outcome... so I must match it as close to perfect as > possible even if that means dropping some data from the 'treatment' > group. > > Here's some code: > > match = matchit(Group ~ Stage + Age + Gender + PS, myData, > method="optimal") > matchedData = match.data(match) > by (matchedData$Stage, matchedData$Group, table) > > matchedData$GP: 0 > > 1 3A 3B 4 > 1 6 9 10 > ----------------------------------------------------------------------- > --------------------------------- > myreData$GP: 1 > > 1 3A 3B 4 > 1 3 9 13 > > Can anyone point me to a method that tells R to prioritise Stage over > the others? > Thanks in advance > > *********************************************************************** > ********************************************* > > This message may contain confidential information. If > yo...{{dropped:19}} > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide http://www.R-project.org/posting- > guide.html > and provide commented, minimal, self-contained, reproducible code. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
