As you appeared to have received no reply ... 1) Use nls() on the original equation
2) Transforming first and using linear fitting is **NOT** the same. The error structures differ and therefore you get different results. The greatest effect is on inferences -- i.e confidence intervals for the parameters: the usual asymptotic intervals would be symmetric based on the original scale, asymmetric based on the transformed. For reasonably well-behaved data the point estimates shouldn't be too much different, however. In any case, the linearization is a good way to find starting values. -- Bert Gunter Genentech Non-Clinical Statistics South San Francisco, CA "The business of the statistician is to catalyze the scientific learning process." - George E. P. Box > -----Original Message----- > From: [EMAIL PROTECTED] > [mailto:[EMAIL PROTECTED] On Behalf Of S.O. Nyangoma > Sent: Wednesday, August 10, 2005 3:22 AM > To: Dan Bolser > Cc: R mailing list > Subject: Re: [R] Question about curve fitting... > > I see that > log(y)=log(k1)+k2*log(x) > use lm? > > ----- Original Message ----- > From: Dan Bolser <[EMAIL PROTECTED]> > Date: Wednesday, August 10, 2005 11:41 am > Subject: [R] Question about curve fitting... > > > > > Meta: > > This question is somewhat long and has two parts, I would be very > > happyfor someone just to nudge me in the right direction with the > > manual / > > tutorial, as I am somewhat lost... > > > > > > 1) How do I fit a curve of the form "y = k1 * x^k2" ? > > > > I want to estimate values of k1 and k2 given the x/y data I have, > > and I > > can't work out how to get R to calculate and return their estimates. > > > > > > 2) Given the value of k1 and k2 for population A, how can I test if > > population B has significantly different values of k1 and k2? > > > > Sorry for the basic question. I think I just need to read > up on a few > > functions. > > > > > > I have about 50 xy pairs in total if that makes a difference. > > > > Dan. > > > > ______________________________________________ > > [email protected] mailing list > > https://stat.ethz.ch/mailman/listinfo/r-help > > PLEASE do read the posting guide! http://www.R-project.org/posting- > > guide.html > > ______________________________________________ > [email protected] mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide! > http://www.R-project.org/posting-guide.html > ______________________________________________ [email protected] mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide! http://www.R-project.org/posting-guide.html
