[R] Confidence Limits for Non-Linear Regression

Douglas Bates bates at stat.wisc.edu
Fri Jan 12 16:09:26 CET 2001

Prof Brian D Ripley <ripley at stats.ox.ac.uk> writes:

> I had thought if you turn tracing on, you would see the area in parameter
> space where profile.nls gets in trouble, but profiling seems to turn it
> off.  You could try increasing maxiter in nls.control.

It works if trace = TRUE in the original call to nls that creates the
object being profiled.  Try

example(Bennett5, package = "NISTnls")
pr2 <- profile(fm2)

Dieter: If you fitting a conventional three parameter logistic model
or a four parameter model you may want to try the self-starting model
functions in the nls package (SSlogis or SSfpl).  Those functions use
a parameterization that has proven to be very stable.  Often the
difficulties in assessing the variability in parameter estimates is
due to a poorly chosen parameterization for the model.

If you would be willing to send me one of the problematic data sets I
could try to assess what is going wrong for you.
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