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st: Calculating duration of time


From   Joseph Coveney <jcoveney@bigplanet.com>
To   Statalist <statalist@hsphsun2.harvard.edu>
Subject   st: Calculating duration of time
Date   Thu, 12 Dec 2002 10:07:36 +0900

Somewhere I had read that it has become a convention to define a duration or interval 
of time as:

end time - start time + 1,

where the 1 is the unit of time used.  Thus, for example, for a common health 
economics measure, the length of hospital stay (LOS) is defined to be discharge date - 
admission date + 1 day.

A patient who is discharged a few hours after admission would have an LOS of one 
day, one who is discharged the day after admission would have an LOS of two days, 
and so on.  I suppose that the motivation for this definition is to remove zeroes from 
durations, since these are often skewed and a logarithmic transformation is used, as for 
example -means LOS, add(1)-.

I thought that I had seen the formula in an online data definition document or data 
standards document at a website for the Center for Disease Control, FDA, HL7 or 
CDISC, but I cannot relocate it.  Apologies for the somewhat off-topic nature of the 
question, but has anyone on the list come across this convention?

Joseph Coveney
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