[R] SSweibull

[Prof Brian Ripley]

On Tue, 26 Jun 2001, [ISO-8859-1] Lüdde Mirko wrote:

> Dear all,
>
> I'd like to use the `SSweibull' function for survival analysis.  In

You would be better off using survreg in package survival (formerly
survival5).

You forgot to mention SSweibull is in package nls, BTW, and intended to be
used by a call to nls().

> order to become acquainted with the function, I said `help(SSweibull)'
> and went through the example. What puzzles me is
>
> 1. What should I make of the assertion `Initial values are in fact the
>    converged values'?
>
> 2. When doing a `SSweibull(Chick.6$Time, Asym, Drop, lrc, pwr)'
>    I can see no indication of convergence of the values whatsoever.
>    On the other hand, plotting the object yields a nice Weibull curve.
>
> 3. Wouldn't it be nice to have some formulas in the help section
>    precisely explaining the meaning of the parameters? There
>    are several parametrizations of the Weibull distribution.

Would you like to submit a patch to the help page (to R-bugs)?  You can
read the R code to find out which was used, or even the help page under
Value:!

>
> Cheers, Mirko.
> --
> Dr. M. Luedde <Mirko.Luedde at CellControl.De>
> CellControl Biomedical Laboratories AG
> Am Klopferspitz 19, 82152 Martinsried
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
University of Oxford,             Tel:  +44 1865 272861 (self)
1 South Parks Road,                     +44 1865 272860 (secr)
Oxford OX1 3TG, UK                Fax:  +44 1865 272595

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