[R-lang] Re: 3 Level IV

[Levy, Roger]

On Feb 12, 2011, at 5:35 PM, Peter Graff wrote:

> Dear R-Lang,
> 
> I have a question about how to code a 3-level IV in a regression.
> 
> The 3 levels are motivated by 2 2-level predictors of theoretical interest (A/B and C/D):
> 
> Level 1: A C
> Level 2: A D
> Level 3: B D
> 
> Is it reasonable to code:
> 
> A versus B, C versus D, Interaction
> 
> Or ist it better to code:
> 
> A v B, AC v AD
> 
> The first coding reflects the theoretical interest more directly, the second coding has considerably less collinearity.

Hi Peter,

I'm having a bit of trouble understanding exactly what you're asking.  Are you considering the use of two different contrast matrices?  If so, what exactly are the contrast matrices you're considering?  And what precisely do you hope to get out of your analysis?

Best

Roger

--

Roger Levy                      Email: rlevy@ucsd.edu
Assistant Professor             Phone: 858-534-7219
Department of Linguistics       Fax:   858-534-4789
UC San Diego                    Web:   http://idiom.ucsd.edu/~rlevy