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.
HTH
Eik
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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