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st: xtabond2: singular covariance matrix

From   Daniel Lee <>
Subject   st: xtabond2: singular covariance matrix
Date   Fri, 14 Jul 2006 07:40:02 -0700 (PDT)


I've been running regressions using xtabond2. But I'm
concerned about the validity of my test results for
the following warning:

Warning: Two-step estimated covariance matrix of
moment conditions is singular.

Does this negate the validity of one-step test



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