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Re: st: egen anycount


From   Maarten Buis <maartenlbuis@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: egen anycount
Date   Wed, 25 May 2011 11:15:38 +0200

On Tue, May 24, 2011 at 9:03 PM, Thomas Speidel wrote:
> The reality is much less picture perfect: a MET value is assigned from a
> published compendium of physical activities. This compendium has a single
> decimal point of precision (just like the last page on the Wikipedia
> article). Of course, if I had a choice I would do the calculations myself,
> thus preserving more accuracy, but I have to rely on published sources and
> work within its constraints.
> I suspect you are going to suggest using reshape... :-)

No, if you want to make use of >= or <= or == evaluations, and you
really care about those equal signs, than you must code those
activities as 10*MET values. These will be integers and thus stored
precisely. The distinction here is between precise measurement (which
you do not have, but the same is true for most of us) and precise
storage. It  is the latter that gave you trouble when you tried to
evaluate -variable >= some number-.

This advise of coding 1.1 as 11 and 1.2 as 12, etc works because you
have exactly one number behind the decimal point. If the numbers
happen to money in euros or dollars and you wanted them to be accurate
up to the cent, you would store those number in 100*dollars or
100*euros (i.e. in cents). The trick is that computers can store
integers exactly, so if there is a fixed number of numbers behind the
decimal point you can store those numbers exactly by multiplying with
the appropriate power of 10 that will turn them into integers.

Hope this helps,
Maarten

--------------------------
Maarten L. Buis
Institut fuer Soziologie
Universitaet Tuebingen
Wilhelmstrasse 36
72074 Tuebingen
Germany


http://www.maartenbuis.nl
--------------------------
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