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

Ben Bolker 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 
by Gomes 

   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]]
> _______________________________________________
> R-sig-mixed-models using r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-sig-mixed-models

More information about the R-sig-mixed-models mailing list