[R] non-linear curve fitting

[Hufkens Koen]

Is their a means of getting an F-statistic (p-value) out of all of this.

Because least-square criterion / r-square only tell me how good the fit is and not necessarily how solid this fit is. An F-statistic (p-value) would be nice...

Regards,
Koen


> -----Original Message-----
> From: Philippe Grosjean [mailto:phgrosjean at sciviews.org] 
> Sent: donderdag 22 maart 2007 14:02
> To: Hufkens Koen; r-help at stat.math.ethz.ch
> Subject: Re: [R] non-linear curve fitting
> 
> Hello,
> 
> If a least-square criterion is fine for you, you should use 
> nls(). For the logistic curve, you have a convenient 
> self-starting model available: 
> SSlogis(). Look at:
> 
> ?nls
> ?SSlogis
> 
> Best,
> 
> Philippe Grosjean
> 
> ..............................................<°}))><........
>   ) ) ) ) )
> ( ( ( ( (    Prof. Philippe Grosjean
>   ) ) ) ) )
> ( ( ( ( (    Numerical Ecology of Aquatic Systems
>   ) ) ) ) )   Mons-Hainaut University, Belgium
> ( ( ( ( (
> ..............................................................
> 
> Hufkens Koen wrote:
> > Hi list,
> >  
> > I have a little curve fitting problem.
> >  
> > I would like to fit a sigmoid curve to my data using the 
> following equation:
> >  
> > f(x) = 1/(1 + exp(-(x-c)*b)) (or any other form for that matter)
> >  
> > Where x is the distance/location within the dataframe, c is 
> the shift of the curve across the dataframe and b is the 
> steepness of the curve.
> >  
> > I've been playing with glm() and glm.fit() but without any luck.
> >  
> > for example the most simple example
> >  
> > x = -10:10
> > y = 1/(1 + exp(-x))
> > glm(y ~ x, family=binomial(link="logit"))
> >  
> > I get a warning:
> > non-integer #successes in a binomial glm! in: eval(expr, envir, 
> > enclos)
> >  
> > and some erratic results
> >  
> > This is the most simple test to see if I could fit a curve 
> to this perfect data so since this didn't work out, bringing 
> in the extra parameters is a whole other ballgame so could 
> someone give me a clue?
> >  
> > Kind regards,
> > Koen
> >  
> > 
> 
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