[R] conditional gap time frailty cox model for recurrent events

Göran Broström goran.brostrom at umu.se
Mon Sep 5 12:06:15 CEST 2016

Dear Elisabetta,

I have no direct answer to your question, but a suggestion: Use the 
'coxme' function (in the package with the same name). In the help page 
for 'frailty' (survival) you will find: "The coxme package has 
superseded this method. It is faster, more stable, and more flexible."

Hth, Göran

On 2016-09-05 11:42, Elisabetta Petracci wrote:
> Dear users,
> I am fitting a conditional gap time frailty cox model weighting
> observations by means of inverse probability time dependent weigths.
> Attached find the self-explaining dataset.
> I have used the following sintax:
> coxph(Surv(gaptstart,gaptstop,status)~treat+strata(nrecord01)+frailty(id,distribution="gamma",method="em"),
> data=dataNOTDrr,weights=dataNOTDrr$weight)
> And I get the following warning:
> Warning message:
> In coxpenal.fit(X, Y, strats, offset, init = init, control, weights =
> weights,  :
>   Inner loop failed to coverge for iterations 3 4
> I have tried to:
> - leave out the weights but I get the error anyway
> - to randomly select a subset of patients and I don't get the error. This
> seems to suggest that the problem is with some observations.
> Any suggestion?
> Many thanks,
> Elisabetta
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