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st: observations differ with lrtest because of interaction terms


From   Meredith Carlson <grlfrendinac0ma@yahoo.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: observations differ with lrtest because of interaction terms
Date   Tue, 18 May 2010 14:13:24 -0700 (PDT)

Hello Stata users,

I'm a Stata rookie, so please bear with me... I'm having problems when I run lrtest with logistic regression to test for interaction between wealth index and region variables.  The number of observations differ, not because of missing values, but because of the interaction terms.  The model including interaction has fewer observations because some have been dropped because of this note...

note: _IsesXreg_3_9 != 0 predicts failure perfectly
      _IsesXreg_3_9 dropped and 4 obs not used


What exactly does this note mean?  What can I do to correct the number of observations so lrtest will run?


Any advice would be greatly appreciated.  Thank you!


      

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