[R] nls, convergence and starting values
patrick.giraudoux at univ-fcomte.fr
Sat Mar 28 10:40:01 CET 2009
Patrick Burns a écrit :
> Patrick Giraudoux wrote:
>> Bert Gunter a écrit :
>>> Based on a simple scatterplot of pourcma vs transat, a 4 parameter
>>> looks like wild overfitting, and that may be the source of your
>>> Given the huge scatter, a straight line is about as much as would seem
>>> sensible. I think this falls into the "Why ever would you want to do
>>> such a
>>> thing?" category.
>>> -- Bert
>> Right, well, the general idea was just to show that the "straight
>> line" was the best model indeed (in the other data sets, with model
>> comparison, the logistic one was clearly shown to be the best... ).
>> Can the fact that convergence cannot be obtained be an acceptable and
>> sufficient reason to select the null model (the straight line) ?
> It is my experience that convergence problems are
> often encountered when the model makes little sense.
> I'm not so sure that non-convergence on its own is
> a good reason to reject the model. That is, to answer
> your specific question, I think it is acceptable but not
> Patrick Burns
> patrick at burns-stat.com
> +44 (0)20 8525 0696
> (home of "The R Inferno" and "A Guide for the Unwilling S User")
OK. Thanks for this opinion. Actually I was sharing it intuitively but
facing such situation for the first time, was quite unconfortable to
make a decision (and still I am). We are touching epistemology... and
maybe a bit far from purely technical thus from the R list issues.
Tanks again, anyway,
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