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Variables --DY, --STDY, and --ENDY represent days relative to the reference start date in RFSTDTC where:

• --DY is the relative study day of the date populated in --DTC for the observation,
• --STDTC is the relative study day of the date populated in --STDTC for the observation; and
• --ENDY is the relative study day of the of the date populated in --ENDTC for the observation.

All study day values will be integers and there will be no study day 0. The reference start date is considered day 1 and the study day value is increased by 1 for each date following the reference start date and decreased by 1 for each date prior to the reference start date, e.g.:

--DY = (date portion of --DTC) - (date portion of RFSTDTC) + 1 if --DTC is on or after RFSTDTC
--DY = (date portion of --DTC) - (date portion of RFSTDTC) if --DTC precedes RFSTDTC

• Study days may be cal

The calculation of additional study days within subdivisions of time in a clinical trial may be based on 1 or more sponsor-defined reference dates not represented by RFSTDTC. In such cases, the sponsor may define supplemental qualifier variables and the Define-XML document should reflect the reference dates used to calculate such study days. If the sponsor wishes to define "day within element" or "day within epoch", the reference date/time will be an element start date/time in the Subject Elements (SE) dataset (see Section 5.3, Subject Elements).