As far as I can tell, Uwe is not even fitting a model, but instead just solving a nonlinear equation, so I don't know why he wants a R^2. I don't see a statistical model here, so I don't know why one would want a statistical measure.
Andy > -----Original Message----- > From: r-help-boun...@r-project.org > [mailto:r-help-boun...@r-project.org] On Behalf Of Bert Gunter > Sent: Friday, March 04, 2011 11:21 AM > To: uwe.wolf...@uni-ulm.de; r-help@r-project.org > Subject: Re: [R] Coefficient of Determination for nonlinear function > > The coefficient of determination, R^2, is a measure of how well your > model fits versus a "NULL" model, which is that the data are constant. > In nonlinear models, as opposed to linear models, such a null model > rarely makes sense. Therefore the coefficient of determination is > generally not meaningful in nonlinear modeling. > > Yet another way in which linear and nonlinear models > fundamentally differ. > > -- Bert > > On Fri, Mar 4, 2011 at 5:40 AM, Uwe Wolfram > <uwe.wolf...@uni-ulm.de> wrote: > > Dear Subscribers, > > > > I did fit an equation of the form 1 = f(x1,x2,x3) using a > minimization > > scheme. Now I want to compute the coefficient of > determination. Normally > > I would compute it as > > > > r_square = 1- sserr/sstot with sserr = sum_i (y_i - f_i) and sstot = > > sum_i (y_i - mean(y)) > > > > sserr is clear to me but how can I compute sstot when there > is no such > > thing than differing y_i. These are all one. Thus > mean(y)=1. Therefore, > > sstot is 0. > > > > Thank you very much for your efforts, > > > > Uwe > > -- > > Uwe Wolfram > > Dipl.-Ing. (Ph.D Student) > > __________________________________________________ > > Institute of Orthopaedic Research and Biomechanics > > Director and Chair: Prof. Dr. Anita Ignatius > > Center of Musculoskeletal Research Ulm > > University Hospital Ulm > > Helmholtzstr. 14 > > 89081 Ulm, Germany > > Phone: +49 731 500-55301 > > Fax: +49 731 500-55302 > > http://www.biomechanics.de > > > > ______________________________________________ > > R-help@r-project.org mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > > and provide commented, minimal, self-contained, reproducible code. > > > > > > -- > Bert Gunter > Genentech Nonclinical Biostatistics > 467-7374 > http://devo.gene.com/groups/devo/depts/ncb/home.shtml > > ______________________________________________ > R-help@r-project.org mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > Notice: This e-mail message, together with any attachme...{{dropped:11}} ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
