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st: Hausman error


From   Marie Olson <marie.olson@wayne.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: Hausman error
Date   Thu, 31 Oct 2002 09:22:15 -0500

I am running a series of analyses using xtlogit.  In order to identify
which method of xtlogit is appropriate, I am using the Hausman test with
xtlogit, fe run first, then xtlogit, re run second.  On occasion, I run
into the problem where the Hausman test produces an assumption error
indicating the following:
 Test:  Ho:  difference in coefficients not systematic

                chi2(  1) = (b-B)'[(V_b-V_B)^(-1)](b-B)
                          =    -0.80    chi2<0 ==> model estimated on
these
                                        data fails to meet the
asymptotic
                                        assumptions of the Hausman test

I was earlier advised to eliminate the cases dropped by the fixed
effects model (due to lack of variation in the dependent variable) for
both analyses, but that did not change the error problem.
Does anyone have any ideas?
Thanks in advance,
Marie

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