Andy, You may well be right. I assumed "fitting an equation" means that he had data to which the equation was being fitted. Maybe that's wrong -- re-reading the post still does not clarify the point for me. In any case, either way, fitting R^2 makes no sense.
-- Bert On Fri, Mar 4, 2011 at 8:44 AM, Liaw, Andy <andy_l...@merck.com> wrote: > 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 attachments, contains > information of Merck & Co., Inc. (One Merck Drive, Whitehouse Station, > New Jersey, USA 08889), and/or its affiliates Direct contact information > for affiliates is available at > http://www.merck.com/contact/contacts.html) that may be confidential, > proprietary copyrighted and/or legally privileged. It is intended solely > for the use of the individual or entity named on this message. If you are > not the intended recipient, and have received this message in error, > please notify us immediately by reply e-mail and then delete it from > your system. > > -- Bert Gunter Genentech Nonclinical Biostatistics ______________________________________________ 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.
