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st: effect coding with interaction variables


From   "Abdul Q Memon" <a.memon@ucl.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: effect coding with interaction variables
Date   Wed, 10 Mar 2010 10:19:04 -0000

Hi

I would like to get some information about effect coding in regression
especially with interaction variables. Any reference or example will be
highly appreciated.
Just to give you an idea about the data which I am using:

I have 5 Road classes, 5 vehicle classes, 24 interaction variables. In
effect coding I am using 4 road classes, 4 vehicle classes and 15
interaction variables. I am coding them as ( 1 if it is comparison group,
0 if it belongs to other 2 groups, -1 if is the 5th group which I am
omitting  as explanatory variable. I am doing the same stuff with 15
interaction variables (1 if it is comparison group, 0 if it belongs to
other 14 groups, -1 if is the reference group which I am omitting as
explanatory variable.

If some can comment or direct me to any relevant example/ literature I
will be highly grateful.
I have also used Devcon but it seems it is not going to work in this case
as in interactions it is having more than one reference category and it is
predicting different values than the original model.

Regards

Memon


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