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st: egen; version

From   David Kantor <>
Subject   st: egen; version
Date   Wed, 25 Feb 2004 16:57:16 -0500

Hi, everyone.

I just noticed a peculiar behavior that I thought I'd share.

If I do this...

gen byte temp1 = V8==.c

egen byte b1 = max(V8==.c), by(V2 V3)
egen byte b2 = max(temp1), by(V2 V3)

Then b1 and b2 can be different, contrary to my initial expectation.

This was a puzzle, but then I realized that egen.ado (and _gmax.ado) set version to 6. Therefore, the expression V8==.c within the call to egen evaluates to 1 for ALL missings -- not just .c. Thus, b1 indicates the presence of any missings in V8, whereas b2 indicates the presence of .c only.

This is something to be aware of, and I didn't see any warning about it in the egen help.

I''ve sent this to Stata tech support, too.
-- David

David Kantor
Institute for Policy Studies
Johns Hopkins University

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