[R] how to adjust link function in logistic regression to predict the proportion of correct responses in 2AFC task?

Prof Brian Ripley ripley at stats.ox.ac.uk
Sat Dec 16 07:01:15 CET 2006

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.


> 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.

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

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