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
[EMAIL PROTECTED] University of Washington, Seattle
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