st: clogit message question

[Julia Gamas <jgamas@mit.edu>]

Hi all,
when running clogit I get the follwing message:
"7618 groups (7618 obs) dropped due to all positive or all negative outcomes."
Can anybody tell me what this means "all positive or all negative outcomes"?
Thank you for any help.
Sincerely,
Julia A. Gamas
Mexico City Project, EAPS
MIT


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