st: dummy dropped in xtgee

["Jessica Kiefte-de Jong" <jessica.de.jong@falw.vu.nl>]

Statalist,

I am using GEE in STATA for analysis of an interventionstudy where data
collection was performed every 6 months and I am assessing time as
categorial variable by using dummies. However, STATA dropped the dummy I
used as reference catagory (Dtime6). How can I fix this problem?

I have used the following command:

xtgee homocysteine intervention Dime6 Dtime12 Dtime 18 Dtime24, i(ppnr)
corr(independent) robust
note: Dtime6 dropped due to collinearity

Thanks in advance,

Jessica


VU University, Amsterdam
The Netherlands


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