[R] Fitting a choice model (Bradley-Terry generalization)

[David Scott]

I have some data I would like to model which involves choice of food by 
dung beetles.

There are a number of experiments  where in each case, there are five 
choices. Overall there are more than 5 different foods being compared 
(including a placebo) and different experiments use different comparisons.

The problem is a generalization of Bradley-Terry but it differs from 
some generalizations in that the comparisons are not pairwise, and they 
don't produce a full ordering, just that one is preferred to the other 
four possibilities.

I have had a look at the BradleyTerry2, eba, pmr and MLCM packages, none 
of which appear to provide the required functionality. I have also 
looked at a number of papers (Hunter, 2004; Firth, 2005; Huang Weng and 
Lin, 2006; and Fujimoto, Hino and Murata 2011). I think fitting using 
maximum likelihood should be possible, but would welcome any pointers to 
useful code,  relevant ideas, or similar analyses.

David Scott