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re: st: -xtmixed- and random terms nested within fixed treatment terms?
Have you seen the very helpful pages on xtmixed at UCLA? They are:
for classical experimental designs:
For the examples in Kreft and de Leeuw's textbook on multilevel
For examples from Singer's paper using SAS but with other mixed model
packages, including xtmixed:
I don't know these answer your question.
I have a uestion on the new xtmixed. I am trying to match a model
run in S-Plux lme, and I am confused by the (lack of) nesting in
Suppose I have subjects assigned to treatment with outcomes
measured at repeated occasions, and a covariate. It seems that the
syntax for -xtmixed- should be something like this, where id
(treatment) indicates nesting of id within treatment:
xtmixed outcome covariate treatment occasion || subject(treatment):
I might expect an adaptation of the example for xtmixed on page 184
[XT] to look like this:
xtmixed weight preweight treatment week || id(treatment):
It seems to me that id must be nested in treatment, but treatment
is a fixed effect, not random, so the following syntax would be
xtmixed weight preweight treatment week || id : treatment
It does not seem possible to nest subject (as a random term) within
treatment in -xtmixed-; which seems the appropriate specification.
Am I incorrect in thinking that this nesting is necessary?
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