Re: st: semiparametric mixture cure models

["E. Paul Wileyto" <epw@mail.med.upenn.edu>]

If you are talking about a Cox-type regression on top of a cure mixture, 
then no.  These have real identifiability problems, and identification 
usually involves making an assumption about where the floor is.
There is strsnmix, Paul Lambert's parametric cure-mixture model, and it 
works well.  I have some home-grown stuff, but it is still parametric.  
If you have trouble with identification using the parametric model, it 
may be because the floor is vague in your data.  Parametric cure models 
fit well if you can actually see the floor in a Kaplan Meier plot.  If 
you do not see the survivorship leveling off in the KM plot, the floor 
of the cure model doesn't have any way to ID the floor in your data.
Have you thought of modeling with frailty?  You may achieve the same 
kind of result with a slightly different set of assumptions.
P



Sridhar Telidevara wrote:
> Are there any stata routines for estimating a semiparametric mixture cure
> model with fixed covariates?  The data have 30,000  observations and the
> duration of observation is in days ( 1 day to 1096 days). 
>
>  
>
> I have estimated several parametric mixture cure models and they did not
> yield good results. Cure percentage was very low, the fit had long tails and
> the median survival time is greater than 1096 days. Therefore, there exists
> an identification problem.
>
>  
>
> Further, 
>
>  
>
> 1.       since the data is in days, is stset enough or episode splitting is
> required?
>
>  
>
> 2.       Convergence problems with the EM algorithm and the bootstrapping
> procedures if the data is in days.
>
>  
>
> 3.       If I have to group the data to estimate a semiparametric mixture
> cure model what is the optimal way to group the data? 5 days, 10 days? 30
> days?
>
>  
>
> Thank you for your help,
>
>  
>
> Sridhar Telidevara
>
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>   
--
E. Paul Wileyto, Ph.D.
Assistant Professor of Biostatistics
Tobacco Use Research Center
School of Medicine, U. of Pennsylvania
3535 Market Street, Suite 4100
Philadelphia, PA  19104-3309

215-746-7147
Fax: 215-746-7140
epw@mail.med.upenn.edu 

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