Hi, Kirill.
The short answer is: Use vglm directly. Thomas may have implemented
this parameterization.
The long answer is:
You can only change the default parameterization in a Zelig model in
certain classes of models. For example a glm model uses family() to
provide an inverse link function for calculating the expected value
from the linear predictor. The multinomial logit model is implemented
via VGAM, which also has a faimly function. If the VGAM link for the
mlogit model supports an alternative parameterization, you can pass it
to the fitting function using ... -- that is, by adding additional
arguments to zelig(...).
Keep in mind, however, that the MLE is invariant to
reparameterization, and direct interpretation of coefficients is
dangerous. Better to simulate the quantities of interest.
Best,
Olivia
---------- Forwarded message ----------
From: Kirill Olegovich Kalinin <kkalinin(a)umich.edu>
Date: Mon, Apr 13, 2009 at 6:03 PM
Subject: alternative parameterization question
To: olau(a)fas.harvard.edu
Cc: olivia.lau(a)post.harvard.edu
Dear Olivia,
I wonder how can I do alternative parameterization with sum of
parameters equal 0 in Zelig?s mlogit model?
Thank you in advance!
Kirill Kalinin
PhD student,
Department of Political Science,
University of Michigan
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