[R] psychometric functions

[Christian Ritz]

Hi Mario,

in many applications there is not much difference between logistic and Gaussian
distributions (just as logit and probit models often produce similar fits)...

Moreover it's possible to fit sigmoidal curves using models such as the (log-)logistic
where the lower and/upper limits are estimated rather than fixed at 0 and 1, respectively.
Have a look at the package 'drc' to see how!

Also the following talk at the recent user! 2008 conference might be of interest to you:

http://www.statistik.uni-dortmund.de/useR-2008//slides/Haubo.pdf


Best wishes
Christian