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st: RE: Precision


From   "Maarten Buis" <M.Buis@fsw.vu.nl>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Precision
Date   Fri, 11 Nov 2005 15:09:43 +0100

StatTransfer has the option to import variables as doubles instead of floats, which are accurate up to 16 digits. 

Do you really need 16 digits? If all the variation occurs in the last digits than you can subtract a very large number like 348080.2688 and than multiply 1000 and you will get the same information with less trouble. Using variables with extremely different variances (e.g. a `normal' variable' with a variance around 1 or 2 and the 16 digit variable with a variance of 1*10^-15) is usually not a good idea in many statistical applications. Stata is usually very good at this, but my gut feeling tells me that 16 digits may be pushing it. If all the variation occurs in the first few digits, than any information in the 16th digit will usually be inconsequential. 

Hope this helps,
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 Ronnie Babigumira
Sent: vrijdag 11 november 2005 12:05
To: statalist@hsphsun2.harvard.edu
Subject: st: Precision

Dear all
I have scanned some of the previous posts on this subject but I am not
making any headway.

I have text file with two variables whose contents are 16 digit numbers
of the form

x
348080.2688552010

I would like to import the data into stata whilst maintainig the
precision. Here is what I have done. I import the variables as strings
and that works. However, the next challenge is that they need to be used
as numeric variables (this is the hair loss part). I have tried

gen y = real(x)
destring x, gen(y)

Both dont have an option to specify the format. Trying to format the
generated variables also wont help since format y %9.11f  gives me the
dreaded red lines and blue lines

invalid %format
r(120);

So my question is how can I change x from string to numeric whilst
maintaining the precision. Or even better, how best can I import this
into stata as a numeric variable without loss of precision.

Ronnie
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