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st: RE: Multicollinerity test in IV regression


From   "Nick Cox" <n.j.cox@durham.ac.uk>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Multicollinerity test in IV regression
Date   Wed, 13 Oct 2004 18:10:10 +0100

I assert that multicollinearity is a property of the 
predictors and does not depend on what
you do with them before, during or 
after any examination of multicollinearity. 

You can look at the structure of relationships 
with -graph matrix-; get numerical summaries 
by using -correlate-; and use -_rmcoll- to 
look further. 

Whether there is some omnibus test of multicollinearity 
I do not know. If there were, it wouldn't necessarily 
be helpful in indicating what to do. 

I have always found it most useful 
to think about the meanings of variables and the 
roles they play in terms of the underlying science.  
That is, reflection often makes it seem unsurprising
that two or more variables are highly correlated, 
so that they tell the same story and only one 
need be recorded. 

However, there are other issues particularly where 
lots of dummies are included. 

Nick 
n.j.cox@durham.ac.uk 

Rozilee Asid
 
> Just to ask one simple question, how do I test for the existence of
> multicollinearity after using ivreg2 command.
> 

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