st: cluster() or svy? (analysis of cluster-randomized trials)

["Michael I. Lichter" <mlichter@buffalo.edu>]

Hello, friends. I have a question about the analysis of data from 
cluster-randomized trials (CRTs). CRTs are experiments where subjects 
are randomly assigned to conditions (control, treatment) based on their 
group membership rather than being assigned individually as is usually 
the case in randomized controlled trials. In my study, the clusters are 
medical practices, so when a medical practice is assigned to a 
condition, all of the eligible patients therein are also assigned to the 
condition. CRTs should be analyzed using methods that take account of 
the clustering in the study design, of course.

My question is this: For CRTs, is there any statistical reason for 
preferring the cluster() option on estimation commands (e.g., regress, 
logit) over the survey commands, or vice-versa? I've used both and the 
results are similar, but the survey commands estimate larger standard 
errors. If the answer is that they're both equally appropriate but 
produce different results because they use somewhat different methods of 
estimation, that's fine.

Thanks.

Michael

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