[R-sig-DCM] Inclusion of interaction without its main effect
marcel.gerds at berkeley.edu
Wed Feb 2 18:48:49 CET 2011
Dear fellow DC modellers,
I want to include an interaction term as an explanatory variable without
having its main effect in the model. For example, I run
mlogit.model <- mlogit ( choice ~ cost_a / income + cost_b , data = data
_ ml )
where two kind of cost are used as explanatory variables for choosing an
alternative. Income is a subject-specific variable. However, if I run
this, R not only includes cost_b and cost_a:income in the model, but
Is there a way to suppress the inclusion of a main effect when one wants
to add only its interaction?
Thanks for any help.
Marcel Gerds, M.Sc.
University of California
Department of Agricultural and Resource Economics
233 Giannini Hall
Berkeley, CA 94720
Tel.: +1 510-643-2202
Mobil: +49 176 21302825
E-Mail: marcel.gerds at berkeley.edu
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