[R-sig-ME] Grouping variables technically suitable for modeling
bbo|ker @end|ng |rom gm@||@com
Tue Nov 9 02:34:35 CET 2021
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
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?)
> Tim M
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