I would suggest a model with a baseline level, something like nls(AMP~E0+(Emax-E0)*Time**gamma/(EC50**gamma+Time**gamma),data=your data, start=list(EC50=50,gamma=2,E0=0.2,Emax=1.2))->mod.test
AIC(mod.test) does improve. Hope this helps. Jun On Wed, Aug 19, 2009 at 5:04 AM, Dani Valverde <daniel.valve...@uab.cat>wrote: > Hello, > I have this data: > Time AMP > 0 0.2000000 > 10 0.1958350 > 20 0.2914560 > 40 0.6763628 > 60 0.8494534 > 90 0.9874526 > 120 1.0477692 > > where AMP is the concentration of this metabolite with time. If you plot > the data, you can see that it could be fitted using a logistic > regression. For this purpose, I used this code: > > AMP.nls <- nls(AMP~SSlogis(Time,Asym, xmid, scal), data = > concentrations,model=T) > > When plotting the fitted function, it seems that it fits quite well at > the end of the time. However, at the beginning it seems that the fit is > not so good. How can I achieve a better fit? Forgive me if it is a > stupid question, but I am just starting with non linear regression. > Thank you, > > Dani > -- > [?] > > ______________________________________________ > 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. > -- Jun Shen PhD PK/PD Scientist BioPharma Services Millipore Corporation 15 Research Park Dr. St Charles, MO 63304 Direct: 636-720-1589 [[alternative HTML version deleted]] ______________________________________________ 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.
