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st: re: different result each time


From   Kit Baum <baum@bc.edu>
To   statalist@hsphsun2.harvard.edu
Subject   st: re: different result each time
Date   Thu, 25 Sep 2008 07:40:35 -0400

< >
Neil said

Your different results may be down to the -merge- you are performing if
one (or indeed both) of the datasets that you are merging does not have
uniquely identifiable observations based on the variable you are merging
on, so check the output after the merge very carefully.


Indeed, this is likely to be the problem. In my book (p.58) there is a section "The dangers of many-to-many merges" that speaks to this very issue. Merges should always make use of the -unique-, -uniqmaster- or - uniqusing- option to prevent some truly bizarre results in the case where the merge keys are not unique in either dataset.

Kit Baum, Boston College Economics and DIW Berlin
http://ideas.repec.org/e/pba1.html
An Introduction to Modern Econometrics Using Stata:
http://www.stata-press.com/books/imeus.html


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