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st: RE: RE: generating a new variable with the egen command


From   "Maarten Buis" <M.Buis@fsw.vu.nl>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: RE: generating a new variable with the egen command
Date   Mon, 28 Nov 2005 16:56:36 +0100

Furthermore, calculating the sums in float format isn't as bad as it initially seems: the fact that Stata shows only 3 digits of precision has to do with the display format. The float is precise up to 8 digits, and is stored that way, as can be seen in the program below.

*-------------------------example------------------
drop _all
input x
	42224464
      67090781
end

egen sum = sum(x)
egen long sumlong = sum(x)

list sum sumlong 

format sum %20.7g

list sum sumlong
*------------end example-----------------

HTH,
Maarten


-----------------------------------------
Maarten L. Buis
Department of Social Research Methodology 
Vrije Universiteit Amsterdam 
Boelelaan 1081 
1081 HV Amsterdam 
The Netherlands

visiting adress:
Buitenveldertselaan 3 (Metropolitan), room Z214 

+31 20 5986715

http://home.fsw.vu.nl/m.buis/
-----------------------------------------

-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu [mailto:owner-statalist@hsphsun2.harvard.edu]On Behalf Of Nick Cox
Sent: maandag 28 november 2005 16:42
To: statalist@hsphsun2.harvard.edu
Subject: st: RE: generating a new variable with the egen command

Your call should be

egen double newvar = ...

or

egen long newvar = ...

If these are integers, -long- is better. Either type
is allowed by the syntax. See the help for -egen- once more.

Nick
n.j.cox@durham.ac.uk

>agostino@unical.it
>
> I'm trying to generate a new variable given by the sum of an
> existing variable
> by year (as I have 2 six month observations for the same
> year) and individual.
> The command is the following:
> egen newvar=sum (oldvar), by(id year)
>
> the problem is that the original values are, for instance:
> 42224464 and
> 67090781, but the sum that STATA computes is 109000000,
> instead of 109315245.
> Why does it round like that?
> The old variable is stored as "double", I have tried to
> change the storage
> type, using recast, but STATA does not allow to do it, as
> many values would be
> changed...



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