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

[John Field]

Hi Daniel,

Sorry, it may have been clearer if I had used 
"subjects" instead of "patients".  The treatments 
were administered to all subjects, and then in 
the succeeding 12 months, some were hospitalised 
and some were not.  Hence only about 25% of the subjects were hospitalised.

The start of the data:
subj    time1   time2   event Treat
1       0       6.2     1       A
1       6.2     12      0       A
2       0       12      0       A

so subject 1 was hospitalised at 6.2 months, subject 2 not at all.

Hope this makes it clearer.
Regards,
John





.At 12:59 PM 31/12/2007, Daniel Malter wrote:
>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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