st: Additive logistic model

[Dorothy Bridges <dbstata@gmail.com>]

I'm wondering whether there's an easy (read: not coding from scratch)
way to estimate an additive logistic model in Stata (like this, for
example: http://gking.harvard.edu/files/abs/trip-abs.shtml; an R
package can be found here http://sekhon.berkeley.edu/robust/).

Essentially, this would require mlogit to read three (or more)
variables representing choice for each observation, rather than just
one categorical variable.  For example: mlogit party1 party2 party3 x,
where each of the party variables records the proportion of votes
obtained by that party in a given district, and x is a vector of
regressors.  (If we had the vote and characteristics of each
individual, of course, this would not be an issue (though I suppose
then there would be bigger issues)).

Many thanks, as always, for your thoughts.
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