[R-lang] Re: 3 Level IV

[T. Florian Jaeger]

Hi Peter,

that depends on your question (the hypothesis that you wish to test).
Multi-collinearity is a consideration that should come in AFTER you've
decided what question to test.

HTH,
Florian

On Sat, Feb 12, 2011 at 8:35 PM, Peter Graff <graff@mit.edu> 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.
>
> Thank you very much,
>
> Peter Graff
>
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