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st: RE: Categorical variable codings

From   "Maarten Buis" <>
To   <>
Subject   st: RE: Categorical variable codings
Date   Thu, 19 Oct 2006 13:50:30 +0200

the -xi3- prefix (see: -findit xi3-) is a convenient way to add your
categorical variables using a variety of different types of contrasts 
and/or two or three way interactions. Which contrasts and interactions
to use is of course dependent on your knowledge of the problem, and 
the question you want to answer.

Maarten L. Buis
Department of Social Research Methodology 
Vrije Universiteit Amsterdam 
Boelelaan 1081 
1081 HV Amsterdam 
The Netherlands

visiting adress:
Buitenveldertselaan 3 (Metropolitan), room Z434 

+31 20 5986715

--- Silwood, Christopher J wrote:
I am trying various regression analyses on data obtained from the
study of 6 different cooking oils, control and 4 different material
treatments, all samples being sampled at 30 min, 60 min and 90 min
heating. I am wondering what a suitable set of categorical variable
codes to use for comparing, e.g. material/time or oil/material/time,
i.e. 5 X 3 or 6 X 5 X 3 at all levels and interactions, assuming with
the latter that "oil" can be included as an independent variable.

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