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st: logistic regression and dropped variable (or error) messages


From   "Wendell Joice" <wjoice@erols.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: logistic regression and dropped variable (or error) messages
Date   Wed, 11 Dec 2002 13:58:38 -0500

Dear statalist,

I am running a series of stepwise logistic regressions using the xi command
and stata 7 (but using stata 6 manuals)
Example:
xi: sw logistic psycther i.race i.ment i.mentlrec i.new i.seenbfr i.acchron
yearnum i.complain if sample==1, pr (.25)

Can anyone explain or direct me to the explanations for the following
messages received in different runs using the same basic command as above ??
(messages received with different variables) (I have tried manuals, findit,
etc. but can't find the explanations...that is, to what specific problems do
the messages refer) :

- "between-term collinearity, variable _Ivar1name_3" (Red error message
followed by r(498) in blue)

- (_Ivar2name_1 dropped due to estimability)

- note: _Ivar3name_2 dropped due to collinearity

- (_Ivar4name_2 dropped because constant)

I think I understand the third one due to collinearity but want to be sure
about the others.

Thanks
Wendell Joice



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