Re: [R] A regression problem using dummy variables

From: Bert Gunter <gunter.berton_at_gene.com>
Date: Thu, 03 Jul 2008 07:21:04 -0700

Contrasts for categorical variables are a technical issue in linear models. They are best understood (imo) as the choice of bases for the vector space of the model matrix. So how good is your linear algebra? A terse but I think very clear treatment of these issues can be found in the relevant chapter of V&R's MASS book.

FWIW, I have found that even statisticians get confused by these issues (certainly I have!).

-----Original Message-----
From: r-help-bounces_at_r-project.org [mailto:r-help-bounces_at_r-project.org] On Behalf Of Ron Michael
Sent: Thursday, July 03, 2008 2:19 AM
To: rlearner309; Peter Dalgaard
Cc: r-help_at_r-project.org
Subject: Re: [R] A regression problem using dummy variables

"which group contrasts you want to look at" can you clarify me on that statement?


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