Hi Milton, you're right that most of the functions in the package "drc" are suited for sigmoidal/s-shaped curves defined on the positive axis.
However, there is one exception: the logistic model: library(drc) sp.coredep.attr.m1 <- drm(preference~dst, data=sp.coredep.attr, fct=L.4()) plot(sp.coredep.attr.m1, log = "") plot(sp.coredep.attr.m1, log = "", xlim = c(-500, 500), ylim = c(0, 1)) summary(sp.coredep.attr.m1) The fit isn't very good, possibly because the curve you've observed seems to have a kind of bent at or close to 0. Christian ______________________________________________ R-help@r-project.org mailing list 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.
