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

[Simon Harmel]

Thank you, this is extremely helpful to know. You mentioned it's well
documented, any possible links to share?

Also, does nlme::lme() behave in the same manner in this regard?

On Fri, Oct 8, 2021 at 4:46 PM Phillip Alday <me using phillipalday.com> wrote:
>
> 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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> >