Dear Statalist,
I have panel-data consisting of 3200 individuals with 4 observations each.
2 of these observations are taken before a treatment, and the other 2 after
the treatment. The dependent variable is bin(0,1).
I wish to calculate the odds ratio before vs. after treatment and I fitted
the following random effects model:
iis idno /* idno=person
identifier (i=1....3200) */
tis obsno /* obsno=observation
number (j=1...4) */
xtlogit depvar treat, re or /* treat=treatment before
and after (t=0,1) */
I used the quadchk command to check whether the quadrature approximation
used for xtlogit,re
was reliable, but for this data the approximation was poor. The panel-level
variance component was high (rho=0.65) indicating that the 4 observations
were highly correlated within each individual, so I thought this may be the
reason why.
Can anyone suggest any alternative methods that I can use to fit this model
in STATA?
Laurence
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