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 -
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?
---------------------------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
*
* For searches and help try:
* http://www.stata.com/support/faqs/res/findit.html
* http://www.stata.com/support/statalist/faq
* http://www.ats.ucla.edu/stat/stata/
