[R] matchit - can I weight the parameters?

[Nordlund, Dan (DSHS/RDA)]

Sorry, Stage should be in quotes in the exact= parameter

match = matchit(Group ~ Stage + Age + Gender + PS, myData, method="optimal", exact=c('Stage'))


Hope this is more 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: Nordlund, Dan (DSHS/RDA)
> Sent: Tuesday, June 19, 2012 4:51 PM
> To: r-help at r-project.org
> Subject: RE: matchit - can I weight the parameters?
> 
> 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-bounces at r-project.org [mailto:r-help-bounces at 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 at 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
> >
> >
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