[R] Mean survival times

[Göran Broström]

On 11/17/05, Christoph Scherber <Christoph.Scherber at uni-jena.de> wrote:
> Dear list,
>
> I have data on insect survival in different cages; these have the
> following structure:
>
>   deathtime status id cage    S      F     G   L     S
>         1.5      1  1 C1      8      2     1   1     1
>         1.5      1  2 C1      8      2     1   1     1
>        11.5      1  3 C1      8      2     1   1     1
>        11.5      1  4 C1      8      2     1   1     1
>
> There are 81 cages and each 20 individuals whose survival was followed
> over time. The columns S,F,G,L and S are experimentally manipulated
> factors thought to have an influence on survival.
>
> Using survfit(Surv(deathtime,status)~cage) gives me the survivorship
> curves for every cage. But what IÂ´d like to have is a mean survivorship
> value for every cage.
>
> Obviously, using tapply (deathtime,cage,mean) gives me mean values, but
> IÂ´d like to have a better estimate of this using a proper statistical
> model. IÂ´ve tried a glm with poisson errors (as suggested in CrawleyÂ´s
> book, page 628), but the back-transformed estimates (using status as the
> response variable and deathtime as an offset) were totally unrealistic.
>
> As IÂ´m new to survival analysis, it would be great if anyone could give
> me some hints on what method would be best.

No method is best, but some methods may be useful ;) One such may be
to fit a parametric model to your data. Check 'survreg'.

GÃ¶ran
>
> Thanks a lot!
> Christoph
>
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--
GÃ¶ran BrostrÃ¶m