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RE: st: Understanding Factor variables - is order significant ?

From   Richard Williams <>
Subject   RE: st: Understanding Factor variables - is order significant ?
Date   Wed, 26 May 2010 08:19:24 -0500

At 03:17 AM 5/26/2010, Jesper Lindhardsen wrote:
Hi All,

Thank you for taking such an interest in my (hairpulling) problem.
I also think it is a bug in -poisson- as there is no other reasonable
explanation for this behaviour in this specific regression command.
I am not able to update Stata/MP to the April edition as it is server
based, so I can't check if that does the trick.
I guess I'll have to hard code the dummy variables until further
clarification .....

If by "hard code" the dummy variables you mean code them so that 0 is the desired reference category, yes, that would work, and might be a good idea even if there was no problem (all these complicated notations may get a little confusing). I wouldn't hard-code the interactions though, as that could cause problems with post-estimation commands like -margins-. You could also just enter the terms in the order that does not cause problems. Or, use ## instead of #. I prefer ## anyway, as it separates the main effects from the interaction effect, and hence you may find that you don't need an interaction term anyway.

Richard Williams, Notre Dame Dept of Sociology
OFFICE: (574)631-6668, (574)631-6463
HOME:   (574)289-5227
EMAIL:  Richard.A.Williams.5@ND.Edu

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