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

[Daniel Malter]

Hi John,

I am on the slow side - can you provide sample code. How can one treatment
group have no admissions? 

Let's say there are treatments W, X, Y, Z. Do you mean that NONE of the
patients who got admitted the first time and, say, received treatment X
during the first admission, have ever had a second admission (in your data).
And for the other treatments W, Y, and Z some of those who got admitted the
first time came in a second time?

Cheers and a happy new year's eve,
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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