st: varlist not allowed error when using xtgee with many interaction terms

[Jordan H <jihool3670@gmail.com>]

Dear all,

I am attempting to run the following model....

xi3: xtgee score i.cohort*i.time*i.content_num, robust

...in which "cohort" has two levels, "time" has three levels, and
"content_num" has ten levels.  Submitting the above code gives me an
error: "varlist not allowed."  However, the model successfully runs
when "content_num" only has eight levels.  To me (a novice when it
comes to the back-end of STATA commands), this seems like there's a
maximum number of variables that xtgee can handle.  Do you think
that's the issue? I've seen a "too many variables specified" error
message in STATA elsewhere so I kinda would expect xtgee to produce a
similar message if there are, in fact, too many (60 total) variables
in the model.

Can you see any way around this issue?

Any and all suggestions are appreciated.  Thank you for the consideration!

Jordan

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