[R] Forcing zero intercept in two predictor case - stat questionnot R question

[John Fox]

Dear Mark,

--------------------------------
John Fox, Professor
Department of Sociology
McMaster University
Hamilton, Ontario
Canada L8S 4M4
905-525-9140x23604
http://socserv.mcmaster.ca/jfox 
-------------------------------- 

> -----Original Message-----
> From: r-help-bounces at r-project.org 
> [mailto:r-help-bounces at r-project.org] On Behalf Of Leeds, Mark (IED)
> Sent: Wednesday, October 03, 2007 5:49 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] Forcing zero intercept in two predictor case - 
> stat questionnot R question
> 
> When one is doing simple regression and needs to force a zero 
> intercept ( for whatever reason. I realize it's a 
> controversial issue ), then subtracting the means of the left 
> hand side and the right hand side from themselves does the 
> trick. Does anyone know if there is a similar trick when the 
> RHS has two variables ? Thanks.

Yes, express all three variables as deviations from their means. (This
follows from the observation that the LS regression surface goes through the
centroid of the variables.)

Regards,
 John