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


From   "Jesper Lindhardsen" <JESLIN01@geh.regionh.dk>
To   <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Understanding Factor variables - is order significant ?
Date   Wed, 26 May 2010 10:17:25 +0200

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 .....

Again thank you,

Jesper
-------------------------------------------
Jesper Lindhardsen
MD, Ph.d. student
Department of Cardiovascular Research
Copenhagen University Hospital, Gentofte
Denmark



-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Richard
Williams
Sent: 26. maj 2010 08:59
To: statalist@hsphsun2.harvard.edu
Subject: RE: st: Understanding Factor variables - is order significant ?

At 12:41 AM 5/26/2010, Kieran McCaul wrote:
>....
>
>It's a bug, I believe.
>
>In the example below there are two dichotomous variables, x1 and x2.
>I declare the reference level for x1 to be x1=1 and leave x2 at its
>default, x2=0.
>
>If I fit x2#ib1.x1, all is well and x1=1/x2=0 is recognised as the
>reference level.
>
>If, on the other hand, I fit ib1.x1#x2, x1=1/x2=0 is recognised as the
>reference level and dropped, but x1=0/x2=0 is also dropped.

Thanks Kieran.  FYI, if you change the -poisson- commands to 
-regress- commands, everything seems to run correctly.  So, if it is 
a bug (which to me seems extremely likely) it is a very quirky bug 
that affects some estimation commands but not others.


-------------------------------------------
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
WWW:    http://www.nd.edu/~rwilliam

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