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st: basic repeated measures question


From   April <aa713407@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: basic repeated measures question
Date   Tue, 17 Nov 2009 12:38:11 -0500

I have 3 questions regarding performing an ANOVA and 1 regarding doing
a repeated measures logistic regression. I have tried to find examples
for my questions but been unsuccessful.

First, my data is setup up like this --

ID     grp     outcome     time
1         1            15             1
1         1            16             2
2         2            12             1
2         2            20             2
3         3            20             1
3         3            12             2
4         4            20             1
4         4            22             2


1. I am interested in whether the change in the continuous outcome
over time significantly differs by group.  How would I setup this
problem in an ANOVA? I would like to obatin the effect of time, group,
and timeXgroup. I tried using repeated measures ANOVA code and this
did not work (refer below)

I wrote -- anova outcome id time grp, repeated(time)
Received this error msg --  could not determine between-subject basic
unit; use bseunit() option
r(422);

2. If timeXgroup is significant, how do I perform simple effects
analysis post hoc in order to understand how the outcome varied by
each group over time and get a graph showing the trends

3. How would I include covariates in the model above essentially?

4. If my outcome was binary rather than continuous, I was interested
in performing xtgee. How would you suggest setting up this code? I
tried to set it up as below, but I did not get the OR for all groups
(one of them was omitted). I believe I am specifying the model
incorrectly.

xtset id
xi: xtgee outcome i.grp, family(binomial) link(logit) eform

Any advice would be appreciated! Many thanks.

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