Hi @SaraA ,
Answered this on your other post but putting the answer here in case someone else comes across the same question:
Because of the nature of the method, REML focuses on variance components and (unlike methods like Least Squares) does not perform standardisation (which is a pre-processing step in the workflow for modelling) - there's a lot of additional complexity with mixed models and trying to standardize them (do you standardise globally or within groups? how do you standardize a variable that is different between two groups?).
Thanks,
Ben
“All models are wrong, but some are useful”