Re: [R] Weibull survival modeling with covariate

From: Thomas Lumley <tlumley_at_u.washington.edu>
Date: Thu 09 Jun 2005 - 23:50:51 EST

On Thu, 9 Jun 2005, Watalu, Y. (aka Wataru) wrote:

> Hi,
>
> I'm also wondering which expression the survreg() uses
> for Weibull regression. Referring to help(survreg) and
> help(survreg.distributions), I guess survreg() fits the
> following model.
>
> survreg() uses a different parametrization, say
> F(x, Wshape, Wscale) = 1-exp(-Wscale*(x^Wshape))),
> and fits a parametric model with these formulas.
> Wshape = 1/"Scale" (calculated by survreg())
> log(Wscale) = model with covariates
>
> Is it correct?
>

Yes. survreg() fits location-scale families to censored data, so the Weibull has to be parametrized as a location-scale family as described above.

         -thomas

Thomas Lumley			Assoc. Professor, Biostatistics
tlumley@u.washington.edu	University of Washington, Seattle

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