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st: RE: Calculating duration of time


From   "Schonlau, Matthias" <matt@rand.org>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   st: RE: Calculating duration of time
Date   Wed, 11 Dec 2002 17:50:17 -0800

This makes sense if time is a  discrete variable 
  e.g. 5th-10th day  where 5 refers to a full day and 10 refers to a full
day
  total time= 6 days
It doesn't make sense if time is continuous.
 e.g. 5th day midnight  -10th day midnight  
  total time = 5 days. 

Matt 


-----Original Message-----
From: Joseph Coveney [mailto:jcoveney@bigplanet.com]
Sent: Wednesday, December 11, 2002 5:08 PM
To: Statalist
Subject: st: Calculating duration of time


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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