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st: RE: RE: zeros in metan


From   "Steichen, Thomas" <STEICHT@rjrt.com>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: zeros in metan
Date   Thu, 17 Oct 2002 12:44:28 -0400

Jodi Segal asked:
  
> > How does stata handle zeros in the denominator for the 
> > metananalysis of relative risks or odds ratios?
 
John Hopkins replied:
  
> > METAN adds 0.5 to all cells of the 2x2 table before 
> > analysis.
   
Nick Cox clarified:

> That is, if and only if _any_ zeros occur in the 2 X 2 table.

And now my 2 cents worth: 

And, if and only if the method is inverse variance or Mantel-Haenszel... 
not true for the Peto method.

Further, per the STB documentation for metan: "However, when 
there are no events in one whole column of the 2x2 table (i.e., 
all subjects have the same outcome regardless of group), the 
odds ratio and the relative risk cannot be estimated, and the 
study is given zero weight in the meta-analysis."

Tom Steichen
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