[R] Restricted 4-PL curves using drc package

[li li]

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
> >
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> >
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