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

From: Daniel Malter <daniel_at_umd.edu>
Date: Sun, 30 Dec 2007 21:29:23 -0500


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

-----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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