[R] Survival analysis with no events in one treatment group

[Daniel Malter]

Hi again,

I meant some rows of sample data, rather than sample code. Sorry about that.

Daniel 


-------------------------
cuncta stricte discussurus
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-----Ursprüngliche Nachricht-----
Von: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org] Im
Auftrag von John Field
Gesendet: Sunday, December 30, 2007 9:16 PM
An: R-help at r-project.org
Betreff: [R] Survival analysis with no events in one treatment group

I'm trying to fit a Cox proportional hazards model to some hospital
admission data.  About 25% of the patients have had at least one admission,
and of these, 40% have had two admissions within the 12 month period of the
study.  Each patients has had one of 4 treatments, and one of the treatment
groups has had no admissions for the period.  I used:

surv.obj<-Surv(time=time1,time2=time2,event=event,type="counting")
model<-coxph(surv.obj~Treatment+cluster(Subject))

and, as explained in the coxph help page, I get a warning message about
convergence because the MLE of one of the coefficients is infinite since
there are no admissions in one group.

I'm looking for suggestions about how to proceed with an analysis of these
data.  I'd prefer not to ignore the fact that there are multiple admissions,
but any alternative ideas I have at the moment do this.

Many thanks,
John Field
=================================
Faculty of Health Sciences Statistical Support Service The University of
Adelaide, Australia 5005

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