# st: RE: Calculating duration of time

 From Joseph Coveney <[email protected]> To Statalist <[email protected]> Subject st: RE: Calculating duration of time Date Tue, 20 May 2003 01:46:28 +0900

```For anyone who has encountered or might encounter this data convention and wonder
about its source, as I did . . .

I posted the following query to the list last December:

-------------------------begin excerpt of posting-------------------------------

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 -

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

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?

---------------------------end excerpt of posting-------------------------------

The convention appears to have been promoted in a U.S. FDA guidance, according to
the following excerpt from a Q & A document (it's on Page 2 of JPMAQ&A01-23-
02revBK.pdf) available on the website of Clinical Data Interchange Standards
Consortium (CDISC) at www.cdisc.org/pdf/JPMAQ&A01-23-02revBK.PDF

------------------begin excerpt of online Q & A document------------------------

2. Submissions Data Model
2.1. Data Convention
Questions:
- Duration values
In FDA guidance, it is mentioned that the following formula should be used to calculate
study day. It isn�t, however, mentioned in Submissions metadata model. Does this
formula also apply in order to calculate the duration of AE [adverse event] occurrence?
And are there any exceptions? If any, what cases are they?
Defined rule in SDM : duration = stop � start + 1

--------------------end excerpt of online Q & A document------------------------

I don't know what FDA guidance document the questioner was referring to.

Joseph Coveney

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