maximum number of levels in proc mixed?

[deleted_user]

Hi all,
How many levels can you incorporate into a multilevel model in SAS proc mixed? Can you have four, e.g. measurements over time nested within patients nested within providers nested within clinics?
Thanks for your help.

[statsplank]

Hi modeler,

Yes, you can have four levels of nested effects. I don't think there is a maximum though keep in mind that PROC MIXED uses iterative estimation algorithm and large number of levels may substantially increase the computation time.