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

From: Calum <>
Date: Mon, 03 Mar 2008 09:16:05 +0000

> Calum wrote:
>> All of that is very nice so far. The I followed bits and pieces of
>> other peoples posts in the past to plot on a weibull regression...
>> > my_curve.Plac <- survreg( Surv(Survival, Censored==0)~
>> TreatmentGroup, subset=TreatmentGroup=="Placebo", data=TestData,
>> dist='weibull')

Peter wrote:
> I'd take a hard look at the pweibull(...) bit. Is "scale" really what
> you want it to be? If coef(my_curve.Pred) is not a scalar, then it gets
> recycled, which could easily cause oscillations.

Aha - found it. Its from my attempt to subgroup the data before I discovered subset... I now have a curve instead of an oscillation. Now possibly that curve is wrong... will need to do more reading!

For reference the line above should read:

   > my_curve.Plac <- survreg( Surv(Survival, Censored==0)~   1, subset=TreatmentGroup=="Placebo", data=TestData,   dist='weibull')

>> 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!

> 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 ;-) mailing list PLEASE do read the posting guide and provide commented, minimal, self-contained, reproducible code. Received on Mon 03 Mar 2008 - 09:25:51 GMT

Archive maintained by Robert King, hosted by the discipline of statistics at the University of Newcastle, Australia.
Archive generated by hypermail 2.2.0, at Mon 03 Mar 2008 - 14:30:18 GMT.

Mailing list information is available at Please read the posting guide before posting to the list.

list of date sections of archive