nlogit / asclogit replicate choice-alternatives per case
my choice desingn includes multiple consecutive choice decisions per
respondent (8 choices á 4 alternatives) and in some cases an
alternative occurs twice per case (in different choice decisions).
This seems to cause problems estimating asclogit and nlogit and the
following error messages occur:
nlogit: "note: 2324 cases (74368 obs) dropped due to no positive
outcome or multiple positive outcomes per case"
asclogit: "variable alternative has replicate levels for one or more
cases; this is not allowed"
(How) Is it possible to estimate asclogit and nlogit with multiple
consecutive choices and replicate alternatives (in different choice
decisions) per case? I have tried estimating both models with only one
choice decision per case (4 alternatives each) which works fine.
Also, when estimating asclogit with effects-type coding the model does
not converge due to collinearity (3 out of 26 parameters are dropped).
asclogit: "note: model has collinear variables; convergence may not be
What would be the best way to deal with collinarity in this case? The
model does not converge when the parameters are kept.
Re: nlogit / asclogit replicate choice-alternatives per case
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I've been looking around the web for an answer to this problem myself, and divined the answer by scrutinizing the restaurant example data set in the nlogit helpfile and comparing it with my own data set. Hopefully I can save you having to go to the same trouble!
The problem is probably in your nlogittree structure. You probably have the wrong variable included for one of the levels in your tree diagram. I'm guessing its the lowest level, as that was my error. The lowest level of your branch structure (i.e. the first variable you specify after the nlogittree command) should be the list of alternatives. That means that it lists a different alternative in every row, repeating the same list of alternatives over and over again for each case in your data set.
In the example above, it is the variable restaurant that is the lowest level of the branch structure.