how to adjust link function in logistic regression to predict the proportion of correct responses in 2AFC task?
On Sat, 16 Dec 2006, baud-bovy.gabriel at hsr.it wrote:
I have would like to use logistic regression to analyze the percentage of correct responses in a 2 alternative forced choice task. The question is whether one needs to take into account the fact expected probabilities for the percentage of correct responses ranges between 0.5 and 1 in this case.
Yes.
Second, how can one implement a link function of the type f(x) = (1+exp(x)/(1+exp(x)))/2 in R?
Looking at make.link() should give you enough to go on.
Third, can it be also done with gee and/or glmm?
For gee, you need to change the C-level internals. (I've done this in the far past for S-PLUS but not for R.) It would be easier to use yags (but I think you still need to dive into the internals). What 'glmm' did you have in mind? Looks like e.g. glmmML and glmmPQL will work with the new link. [...] Someone may have been here already: e.g. http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1434755
Brian D. Ripley, ripley at stats.ox.ac.uk Professor of Applied Statistics, http://www.stats.ox.ac.uk/~ripley/ University of Oxford, Tel: +44 1865 272861 (self) 1 South Parks Road, +44 1865 272866 (PA) Oxford OX1 3TG, UK Fax: +44 1865 272595