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 [EMAIL PROTECTED] University of Washington, Seattle
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