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Re: st: Preventing double counting


From   brendan.halpin@ul.ie (Brendan Halpin)
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Preventing double counting
Date   Wed, 07 Dec 2011 23:47:37 +0000

On Wed, Dec 07 2011, Michael Betz wrote:

> Does anyone have any
> suggestions about how I could get rid of the second observation that
> gives me the negative net migration of the first observation?

If the data is consistent and full (all pairs in the data), then 

keep if orig_state < dest_state

will throw away the redundant half (and the uninformative diagonal).

My instinct, however, would be to test the assumptions of consistency
(i.e. Mij = - Mji) and the presence of all pairs. A simple test would be
to repeat the exercise with

keep if orig_state > dest_state

and checking that you get identical data (with the sign reversed).

Brendan



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