Hi all,
In drc package, is there a function which can be used to fit restricted
4PL curves? For example, we restrict two 4PL curves have the same lower and
upper asymptotes?
Thanks for the help in advance!
Hanna
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1. Don't know, but, assuming I understand you correctly, probably not. 2 Note (subject to my understanding again) that you can rephrase your query as fitting a 4 parameter logistic to all the data together with a grouping factor to indicate the separate curves, allowing two of the parameters (e.g. ED50 and slope) to vary by group. You can then use standard nonlinear fitting (e.g. via the optimx package) to fit the model. Note that you will have to specify 2c +2 starting values for c curves. With c "large" (?whatever that means), this may make convergence tricky. If you care to reply, please do so to the list, not to me. Cheers, Bert Bert Gunter "The trouble with having an open mind is that people keep coming along and sticking things into it." -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) On Wed, Dec 9, 2015 at 12:27 PM, li li <hannah.hlx at gmail.com> wrote:> Hi all, > In drc package, is there a function which can be used to fit restricted > 4PL curves? For example, we restrict two 4PL curves have the same lower and > upper asymptotes? > Thanks for the help in advance! > Hanna > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > 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.
The option 2 works. Thanks. Hanna 2015-12-09 16:24 GMT-05:00 Bert Gunter <bgunter.4567 at gmail.com>:> 1. Don't know, but, assuming I understand you correctly, probably not. > > 2 Note (subject to my understanding again) that you can rephrase your > query as fitting a 4 parameter logistic to all the data together with > a grouping factor to indicate the separate curves, allowing two of the > parameters (e.g. ED50 and slope) to vary by group. You can then use > standard nonlinear fitting (e.g. via the optimx package) to fit the > model. Note that you will have to specify 2c +2 starting values for c > curves. With c "large" (?whatever that means), this may make > convergence tricky. > > If you care to reply, please do so to the list, not to me. > > Cheers, > Bert > > > > > Bert Gunter > > "The trouble with having an open mind is that people keep coming along > and sticking things into it." > -- Opus (aka Berkeley Breathed in his "Bloom County" comic strip ) > > > On Wed, Dec 9, 2015 at 12:27 PM, li li <hannah.hlx at gmail.com> wrote: > > Hi all, > > In drc package, is there a function which can be used to fit restricted > > 4PL curves? For example, we restrict two 4PL curves have the same lower > and > > upper asymptotes? > > Thanks for the help in advance! > > Hanna > > > > [[alternative HTML version deleted]] > > > > ______________________________________________ > > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > > 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. >[[alternative HTML version deleted]]