Laura Bonnett wrote:> Dear R-listers,
>
> I know that there have been many, many posts on the output from
> Survreg. To summarise what I have read, Scale is 1/shape of the
> Weibull which is also the standard deviation of the normal
> distribution which is also the standard deviation of the log survival
> time and Intercept is log(scale). I also know that the hazard
> function can be calculated from the output to give something like:
> h(time)=exp(-intercept)^scale x scale x time^(1-scale)
> So, for example if the intercept was -1.11 and the scale was 1.17 then
> the hazard function is h(t) = exp(1.11)^1.17 x 1.17 x t^0.17 = 4.30
> t^0.17
>
> However, how can I work out what the hazard is I.e. by how much does
> the risk of death increase or decrease with time? Some people have
> said that is the scale parameter is greater than 1 then the risk of
> death increases with age. Is this correct?
>
> I am also aware that Harrell has posted previously that there is a
> case study in his book. I have a copy of the book and have read all
> the case studies but I'm still not convinced I know what the hazard of
> death is?!
library(Design)
f <- psm(...)
h <- Hazard(f) # fitted hazard function as an R function
h # look at it
Evaluate h at any time and any linear predictor (the latter being
computed by for example predict(f, newdata)).
Frank
>
> Sorry that this relates to previously posted queries, but as yet there
> doesn't seem to be a satisfactory solution to the question of the
> output?
>
> Thank you for your help as always,
>
> Laura
>
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--
Frank E Harrell Jr Professor and Chair School of Medicine
Department of Biostatistics Vanderbilt University