[R] survreg with gamma distribution: re-post

[Roger Dungan]

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?

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