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.
*
* For searches and help try:
* http://www.stata.com/help.cgi?search
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
