st: analyzing clustered data

["Cathy L. Antonakos" <cathya@umich.edu>]

I have survey data from medical workers in ICUs. There are 462 surveys altogether, from 25 ICU's, in 8 hospitals. There is no explicit survey sampling plan, so I believe I have to choose between using multilevel modeling, and using clustered robust standard errors (ref: UCLA Stata Library "Analyzing Correlated (Clustered) Data"). I am planning to use clustered robust standard errors. (The intra-class correlation is .24.)

Although most of the variables in the regression model are at the level of medical worker, there are 3 that are not. Two are ICU-level variables (unit type, average patient risk score), and one is hospital-level (hospital size).

I have little experience with this, so I am wondering if the following is correct.
(1) Get robust standard errors by identifying "ICU" as the main clustering variable. 
(2) Include in the regression model the variables "unit-type," "average patient risk score" and "hospital size" as control/independent variables.

It's the 2nd point I'm really unsure about.

Thanks in advance for any advice you can provide.

Cathy Antonakos

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