[R] testing parallelism of does-response curves using package "drc"
arrayprofile at yahoo.com
Tue Mar 16 23:15:40 CET 2010
Thanks for pointing out this great package "drc".
Can you or anyone please help me to specify a constrained 5 PL model where only the transition parameter ("e" in L.5()) are allowed to differ?
BTW, what does the argument "pmodels=" do in the model specification? And what about arguments "lower=" and "upper="? I feel they might be related to specifying constrained models.
--- On Sat, 3/13/10, Eik Vettorazzi <E.Vettorazzi at uke.uni-hamburg.de> wrote:
> From: Eik Vettorazzi <E.Vettorazzi at uke.uni-hamburg.de>
> Subject: Re: [R] testing parallelism of does-response curves using nls()
> To: "array chip" <arrayprofile at yahoo.com>
> Cc: r-help at r-project.org
> Date: Saturday, March 13, 2010, 9:12 AM
> Hi John,
> you may have a look at the drc-package (or look at the
> maintainers web
> site www.bioassay.dk)
> I think it does exactly what you want.
> array chip schrieb:
> > Hi, I am trying to use F test or Chi-square test to
> test if 2 5-parameter (A, B, xmid, scal and H) logistic
> curves are parallel based on residual sum of squares.
> > What's usually done is to first fit the 2 curves using
> a constraint (or global) model where all parameters are kept
> the same except for "xmid"; then fit 2 independent curves
> using unconstraint models where all 5 parameters are allowed
> for change. The extra residual sum of squares can then be
> used to test parallelism using either Chi-square or F test.
> > Now, fitting 2 separate curves are straight forward
> using nls(), but how to fit a global model to only allow
> "xmid" to be different among the 2 curves?
> > BTW, is there a selfStart function for 5-parameter
> logistic like SSfpl for 4-parameter logistic function?
> > Thanks very much,
> > John
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