[R] Fitting a cumulative gaussian

[Dieter Menne]

Gamer, Matthias <gamer <at> uni-mainz.de> writes:

> Specifically, I have data from a psychometric function relating the 
> frequency a subject's binary response (stimulus present / absent) to the 
> strength of a physical stimulus. Such data is often modeled using a 
> cumulative gaussian function. 

Well, more often by a logistic function, and there are quite a few tools
powerful for doings this around, for example glm, or lmer/lme4, glmmPQL/MASS,
glmmML/glmmML . The latter three are the tools of choice when you have within
subject repeats, as it's standard in psychophysics. See
http://finzi.psych.upenn.edu/R/Rhelp02a/archive/33737.html for a comparison.

If you really want a cumlative gaussian, you can misuse drfit/drfit, which is
primarily for dose/response curves and ld50 determination. I think there is a
fitdistr/MASS example around (somewhere in the budworms chapter), but I don't
have the book at hand currently.

Dieter