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.
