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re: st: covariance structure name?
No, I did not frame the question with regard to a specific Stata
command...but your answer did help in that regard.
Please note that this is a stats question and not a Stata question;
which is the purpose of the list. If you have a stats question try
It would seem you have a autoregressive structure. The autoregressive
correlation model formalizes the idea that the magnitude of
correlation among observations "decays" or "drop off" as they become
The six measures were from consecutive minutes over a six minute
interval. Mouse behavior was measured. Multiple mice are each tested
under a saline and two drugs. Replicate mice are nested in 20
isogenic lines, where lines are nested in two genotype classes. The
effect of genotype on drug response was of interest. I used a sum of
the behavior measure across all six minutes, and ran the following
xi: xtmixed sum_6_min i.drug*i.genotype || strain: || mouse:
This is fine since I was not really interested in the time aspect of
the 6 measures, but I was thinking about running the model on the raw
data. My question was really about the setting of the cov() option in
xtmixed should I decide to try this.
I thought autoregressive had the same variances along the diagonal.
In any case, I think it is moot since I only see unstructured as an
alternative in xtmixed.
Where is MedStats? I could not find a google link that seemed to make
sense. I would like a good statistics listserv for questions about
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