[R-lang] Fwd: Simple effects with lmer

[Claire Delle Luche]

Dear R-lang users,

I need to do simple effect analyses for a mixed model.
I started with what was discussed here:
http://pidgin.ucsd.edu/pipermail/r-lang/2009-December/thread.html#202

My model, however, is slightly different: 5 predictors, and one interacts
significantly with two predictors (one has 2 levels, one 3). Predictors with
2 levels were centered, the others were ordered.
It was suggested to do a contrast treatment for both predictors in
interaction, and I assumed I had to run my final model and just replace the
original predictors with the contrast treatment.

QUESTION 1: Is it the right thing to do, or shall I run a model with just
the interaction?

This works fine with the 2*2 interaction, with an acceptable correlation
between the predictors and the interaction
.
For the second interaction however, this is not working: I had to
residualize terms of the interaction to remove collinearity, and, obviously,
contrast treated variables now are still highly collinear.

QUESTION 2: What is the next step to have simple effects for this
interaction? Can we residualise contrast treated predictors?

I really hope this makes sense.
Many thanks for your input.

Best,

Claire Delle Luche
Research fellow
University of Plymouth
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