Re: [R] Problem plotting curve on survival curve (something silly?)

From: Peter Dalgaard <P.Dalgaard_at_biostat.ku.dk>
Date: Mon, 03 Mar 2008 15:17:38 +0100

Calum wrote:
>>> Also is it possible to get an R-squared type value for the fit of
>>> this curve from someplace?
>>>
>>> Finally (three questions in one!) the first two censored data points
>>> (1 in each group) are actually lost to follow-ups. Should they be
>>> marked differently from censored?
>>>
>> Customarily they are not. (I'm sure it is possible to speculate at
>> length about it, though.)
>>
> Going off topic a bit - but did you mean customarily they are not
> censored or customarily they are not handled differently from censored!
>
Customarily not marked differently from other kinds of censoring. (The censoring date has to be "last day known alive", of course.)
>
>> Nothing spectacularly incompetent this far... (I'm not happy with R^2
>> measures outside of linear models, or even within linear models, but
>> several well-reputed people do find them useful, so who am I to bicker?)
>
> I'm not competent to argue. But are you suggesting there is a better
> way to assess fit of the line to the data? Thats what I want - Not
> being a statistician I'm not fussed how its done. But If I'm going to
> extrapolate a line I'd like to know its a reasonable fit first (is
> that purely by eye?) There is a p value reported by survreg but no
> idea how to interpret it ;-)
>
Now there's the first problem... For survival models, the R^2 measures which I have heard of, measure the predictability of the outcome, rather than the discrepancy between observed and expected survival curves. I'm not aware of nice goodness of fit procedures for survival curves (others on the list might be) .

-- 
   O__  ---- Peter Dalgaard             Ă˜ster Farimagsgade 5, Entr.B
  c/ /'_ --- Dept. of Biostatistics     PO Box 2099, 1014 Cph. K
 (*) \(*) -- University of Copenhagen   Denmark          Ph:  (+45) 35327918
~~~~~~~~~~ - (p.dalgaard_at_biostat.ku.dk)                  FAX: (+45) 35327907

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