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!). -- Bert Gunter -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Ron Michael Sent: Thursday, July 03, 2008 2:19 AM To: rlearner309; Peter Dalgaard Cc: r-help@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? --- On Thu, 3/7/08, Peter Dalgaard <[EMAIL PROTECTED]> wrote: ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.
