difficulties with MuMIn model generation with coxph

Message: 131
Date: Mon, 24 Oct 2011 17:08:41 -0700 (PDT)
From: sgilbert<sophielgilbert at gmail.com>
To:r-help at r-project.org
Subject: [R] difficulties with MuMIn model generation with coxph
Message-ID:<1319501321733-3935078.post at n4.nabble.com>
Content-Type: text/plain; charset=us-ascii

Hi All,

I'm having trouble with the automatized model generation (dredge) function
in the MuMIn package. I'm trying to use it to automatically generate subsets
of models from a global cox proportional hazards model, and rank them based
on AICc. These seems like it's possible, and the Mumin documentation says
that coxph is supported. However, when I run the code (see below), it gives
me the following error message:

Error in UseMethod("logLik") :
   no applicable method for 'logLik' applied to an object of class "logical"

##RCode

#read in the data

data1<-read.table('MaleData500.csv', sep=',', header=T)

survival<-Surv(data1$Wks.at.dth, data1$Died)

#create the full (global) model, a coxph object

globemodel<-coxph(survival~  edgeden + pctroad + pctcc90+ pctcc80 +

pctcrsog +  ravine + canfrag + pctoldc,  data=data1)

#evaluate all subsets of models using dredge

exhausting<-dredge(globemodel, eval=TRUE, fixed=c("pctroad"),m.max=3,

marge.ex=TRUE, rank="AICc")

Error in UseMethod("logLik") :
   no applicable method for 'logLik' applied to an object of class "logical"


any suggestions would be greatly appreciated. The globemodel works on its
own, and prints out a summary just fine. The only thing I can think of is
that in the names of globemodel, there is an attribute called loglik, not
logLik?

Thank you,

Sophie