Re: [R] Logistic regression

From: Dieter Menne <dieter.menne_at_menne-biomed.de>
Date: Mon, 14 Apr 2008 20:01:02 +0000 (UTC)

Guillaume Brutel <guillaume.brutel <at> yahoo.fr> writes:

> I am trying to fit a non linear regression model to time series data.
>
> If I do this:
> reg.logis = nls(myVar~SSlogis(myTime,Asym,xmid,scal))
> I get this error message (translated to English from French):
> Erreur in nls(y ~ 1/(1 + exp((xmid - x)/scal)), data = xy, start =
> list(xmid = aux[1], :
> le pas 0.000488281 became inferior to 'minFactor' of 0.000976562

If it occurs after a few iterations (was it verbose=TRUE; sorry, no docs at hand), almost always means that there is no unique solution. Are you sure that your data level out at 1? Or is a normalization factor needed? Try to repost with the original data set if possible. This error message might also turn up when the start values were totally off, so try to plot the curve and the data with the start values.

Setting minFactor never helped for me in that case.

Dieter



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