
On Jan 12, 2013, at 5:04 PM, Ahmed Attia wrote:

> So what is the best method to test the goodness of fit in nonlinear  
> models?

Did you read the citation offered?

-- 
David.
>
> On Sat, Jan 12, 2013 at 4:34 PM, David Winsemius <dwinsemius@comcast.net 
> > wrote:
>
> On Jan 12, 2013, at 3:30 PM, Ahmed Attia wrote:
>
> Please help getting the R squared value in asymptotic regression model
>
> I use the code below
>
> model1<-nls(GN1~SSasymp (nrate,a,b,c), data = data.1 )
>
> and R produced the modell coefficients without the R squared value?
>
> What makes you think there should be an R^2 value?
>
> From the archives:
> https://stat.ethz.ch/pipermail/r-help/2002-July/023461.html
>
> http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2892436/
>
> From the background section to that article:
>
> "Although it is known now for some time that R2 is an inadequate  
> measure for nonlinear regression, many scientists and also reviewers  
> insist on it being supplied in papers dealing with nonlinear data  
> analysis. Several initial and older descriptions for R2 being of no  
> avail in nonlinear fitting had pointed out this issue but have  
> probably fallen into oblivion [2-8]. This observation might be due  
> to differences in the mathematical background of trained  
> statisticians and biochemists/pharmacologists who  often apply  
> statistical methods but lack detailed statistical insight."
>
> -- 
>
> David Winsemius, MD
> Alameda, CA, USA
>
>
>
>
> -- 
> Ahmed M. Attia
>
>
> Research Assistant
> Dept. Of Soil&Crop Sciences
> Texas A&M University
> ahmed.attia@ag.tamu.edu
> Cell phone: 001-979-248-5215
>

David Winsemius, MD
Alameda, CA, USA


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