[R-sig-ME] Grouping variables technically suitable for modeling

[Thierry Onkelinx]

Dear Timothy,

I would expect in your example that the combined effect of ID1 and ID2 will
be more or less equally split over ID1 and ID2. As this would yield a lower
penalty then attributing the effect fully to either ID1 or ID2. Hence the
random effect variances of 1|ID1/ID2 will be a lot smaller than 1|ID1 or
1|ID2.

As ID2 defines almost the same grouping as ID1, it doesn't make sense to
include both of them in the model.

I have no reference at hand for this. Just common sense.

ir. Thierry Onkelinx
Statisticus / Statistician

Vlaamse Overheid / Government of Flanders
INSTITUUT VOOR NATUUR- EN BOSONDERZOEK / RESEARCH INSTITUTE FOR NATURE AND
FOREST
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Op di 9 nov. 2021 om 15:19 schreef Timothy MacKenzie <fswfswt using gmail.com>:

> Dear Ben,
>
> Thank you for sharing the references regarding my first question.
>
> Regarding my second question, I simply mean if we have say ID1 and ID2,
> then for ID2 to be distinguishably nested in ID1, it needs to have a
> different unique categories relative to those of ID1.
>
> For example, if ID1 has 120 unique categories and ID2 has 130
> unique categories nested in ID1, then the variance components for ID1 and
> ID2 are not distinguishable from each other. As a result, only one of them
> can be added as a random effect; either (1 | ID1) or (1 | |ID2), but not (1
> | ID1/ID2).
>
> Is this correct and is there a published reference confirming or
> disconfirming this?
>
> Thanks,
> Tim M
>
> On Mon, Nov 8, 2021 at 7:35 PM Ben Bolker <bbolker using gmail.com> wrote:
>
> >
> >     This is a bit of a "how long is a piece of string" question ...
> >
> >
> >    The "5-6 levels of a grouping variable" rule of thumb is quoted in
> > various places: a variety of those references (Gelman and Hill 2006,
> > Kéry and Royle 2015, Harrison et al 2018, Arnqvist 2020) are collected
> > by Gomes
> > (https://www.biorxiv.org/content/10.1101/2021.04.11.439357v2.full).
> >
> >    I sort of see what you mean by your second paragraph, but can you
> > give an example?
> >
> >
> > On 11/7/21 5:20 PM, Timothy MacKenzie wrote:
> > > Dear Experts,
> > >
> > > Apologies if this question has come up before. But I'm looking for
> > > published references that provide guidance on when one or more grouping
> > > variables that theoretically need to be random factors can also
> > > "technically" be used as random factors?
> > >
> > > For example, I have heard for a grouping variable to be technically
> taken
> > > as a random factor, it needs to have at least 10 or so unique
> categories?
> > > (Any reference to confirm or disconfirm this?)
> > >
> > > For example, I have heard for two grouping variables to be technically
> > > taken as random factors, they each need to have a sufficiently
> different
> > > number of unique categories relative to the other one. Otherwise, their
> > > variance components can't be distinguished from one another and thus
> only
> > > one of them can be taken as random, not both (Any reference to confirm
> or
> > > disconfirm this?)
> > >
> > > Thanks,
> > > Tim M
> > >
> > >       [[alternative HTML version deleted]]
> > >
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