I have a question about how to test a level three effect with a very small N. I hope someone can help. I have a basic, three-level nested design (longitudinal data collected from students nested within classrooms). My problem is that I only have four classrooms. It seems that I can not test for the effect of classroom assignment in level three with this small size. Can I put the classroom effect in at level 2? I am not sure how to handle this issue, but believe I am attempting to use the right analytic technique. Any suggestions would be appreciated.
My intention was to do what you suggest. However, I was told by someone that that wasn't appropriate and perhaps I should run four 2-level models (one for each classroom) and compare the coefficients from each. Do you know of any reference saying what you suggest is okay to do? Thanks for your feedback
I wanted to add a detail about my problem, in case it makes a difference. It's not just that I have a small number of classrooms, 4. I have 1 control classroom and 3 experimental rooms. I think the 1 control room may be the reason I can't run a 3-level model. Anymore input on the best way to test the classroom effect would be great.
Boliang Guo posted on Thursday, November 02, 2006 - 8:05 am
in this case, you can use 1 binary vaaibel indicating control and treatment class, 1 for treatment, 0 for control, as l2 variable in your analysis.
Regarding your Nov 1 post, running four 2-level models separately is useful, but you certainly also want to analyze the four groups together - either using a multiple-group approach or with group as covariates. For a reference regarding choice between these two approaches, see e.g. my 1989 Psychometrika article on heterogeneity; it is not discussing the 2-level case, however.