[R] survreg with gamma distribution: re-post

Thomas Lumley tlumley at u.washington.edu
Thu Feb 24 17:42:53 CET 2005


On Thu, 24 Feb 2005, Roger Dungan wrote:

> Dear r-help subscribers,
>
> A couple of weeks ago I sent the following message to the r-help mail
> list. It hasn't generated any response, and I could really use some help
> on this. Anyone able to help?
>

You can't easily fit a gamma distribution with survreg() unless it has 
known shape parameter.  survreg() fits location-scale models, optionally 
with log transformation, and the gamma family is not one of these.

 	-thomas




> Thanks again,
>
> Roger Dungan
>
>>>
> I am working on some survival analysis of some interval censored failure
> time data in R. I have done similar analysis before using PROC LIFEREG
> in SAS. In that instance, a gamma survival function was the optimum
> parametric model for describing the survival and hazard functions. I
> would like to be able to use a gamma function in R, but apparently the
> survival package does not support this distribution. I have been
> googling around for some help, and have found some threads to a similar
> question posted to the R-Help list in October last year. Because I am a
> bit of a survival analysis and R newbie, I didn't really understand the
> discussion thread.
>
> I've been working with a Weibull distribution, thus:
>
>> leafsurv.weibull<-survreg(Surv(minage, maxage, censorcode, type =
>> "interval")~1, dist = "weib")
>
> And I guess I'd like to be able to do something that's the equivalent of
>
>> leafsurv.gamma<-survreg(Surv(minage, maxage, censorcode, type =
>> "interval")~1, dist = "gamma")
>
> At least one of the R-help listserver comments mentioned using
> survreg.distributions to customise a gamma distribution, but I can't
> figure out how to make this work with the resources (intellectual and
> bibliographical!) that I have available.
>
> With thanks in advance for your help,
>
> Dr Roger Dungan
> School of Biological Sciences
> University of Cantebury
> Christchurch, New Zealand
> ph +64 3 366 7001 ext. 4848
> fax +64 3 354 2590
>
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Thomas Lumley			Assoc. Professor, Biostatistics
tlumley at u.washington.edu	University of Washington, Seattle




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