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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 - 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/

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