[R] Coefficient of Determination for nonlinear function

From: Uwe Wolfram <uwwo_at_in-chemnitz.de>
Date: Fri, 04 Mar 2011 14:42:24 +0100

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 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

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Received on Fri 04 Mar 2011 - 13:44:55 GMT

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