[R-sig-ME] Why || doesn't zero out the correlations in lmer

[Phillip Alday]

This is a well-documented issue: || doesn't zero correlations between a
categorical variable's levels. As far as I know, there are
software-development/technical reasons for this, not statistical ones.

The afex package has an implementation that zeroes everything out.

On 8/10/21 4:32 pm, Simon Harmel wrote:
> Dear Colleagues,
> 
> I have a 'factor' predictor called 'type' (with 4 levels). In the
> random part, I have used `||` so the levels of 'type' can't correlate
> with each other.
> 
> But I wonder why still correlations are reported in the output?
> Thanks, Simon
> 
> lmer(y~type + (type || ID), data = data)
> 
> Random effects:
>  Groups   Name  Std.Dev. Corr
>  ID     type0 0.4276
>           type1 0.7012   0.81
>           type2 0.7115   0.72 0.97
>           type3 0.7655   0.83 1.00 0.98
> 
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