Dear Brian, Thanks for your prompt response. I had tried both 'relevel' and 'reorder' preg_fyear5a.msm<-msm(outcome~ipi, subject=id, data, qmatrix=crudemat, exacttimes=TRUE, covariates=~factor(relevel(year5a),1))
preg_fyear5a.msm<-msm(outcome~ipi, subject=id, data, qmatrix=crudemat, exacttimes=TRUE, covariates=~factor(reorder(year5a),1)) But after reading your suggestion I tried it again in other forms... The following worked for me: preg_fyear5a.msm<-msm(outcome~ipi, subject=id, data, qmatrix=crudemat, exacttimes=TRUE, covariates=~relevel(factor(year5a),1)) I also found out that factor use a range with the first factor (i.e., 1) representing the first item (in my case 0) - so I had to add 1 to use the value 1 as the reference group. Yay! Jase -----Original Message----- From: Prof Brian Ripley [mailto:[EMAIL PROTECTED] Sent: Tuesday, 13 November 2007 10:10 PM To: Jason Ferris Cc: r-help@r-project.org Subject: Re: [R] FW: Reference category for explanatory factors On Tue, 13 Nov 2007, Jason Ferris wrote: > (Oops first mistake was posting to the wrong area) > > I am not sure what is needed to be posted in terms of what I have done > but will explain nonetheless. > > I am using the msm.package and trying to specify my reference category > for an outcome covariate. The following command line works: > > ## age of respondent - using year5a: categorical > preg_fyear5a.msm<-msm(outcome~ipi, subject=id, data, qmatrix=crudemat, > exacttimes=TRUE, covariates=~factor(year5a)) > > However, in the dataset (data) the reference category 0 is a moderately > small cell, so I would like to change it to 1 which is much large. > There are 5 categories in the covariates year5a (0,1,2,3,4). > > I have tried all sorts of approaches with 'ordered' and 'level' but no > love. Which is of not much use to us, as we don't know what you tried nor what went wrong. See ?relevel ?contr.treatment (see 'base') ?C (to specify a contrast for a term) > > Cheers, > > Jase > > PS. Operating in Win XP on a fast machine! > > Jason Ferris > Research Officer > Australian Research Centre in Sex, Health and Society > Level 1, 215 Franklin St > Melbourne > VIC 3000 > P: 61 (0)3 9285 5282 > F: 61 (0)3 9285 5220 -- Brian D. Ripley, [EMAIL PROTECTED] Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595 ______________________________________________ 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.
