Representing References and Relative Timing

Timeframes, fixed points in time, and other milestones may be defined in the context of a study as references to which the timing of other collected observations is related. In such cases, timeframes are referred to as reference periods and such fixed points in time and milestones are referred to as reference time points.

Timing Relative to Reference Periods and Dates

The start and end dates (and times when applicable) of an applicant-defined reference period for a study are represented using variables RFSTDTC and RFENDTC respectively in the Demographics (DM) domain. Applicants may also define dates/times, in addition to a study reference period, from which to reference the relative timing of observations. In both cases, such dates are used as references from which to populate the variables below.

Num	Variable Population	Implementation
1	Days Relative to the Reference Start Date	Variables --DY, --STDY, and --ENDY represent the timing of observations in days relative to the reference start date in RFSTDTC where the value of: --DY is the relative day of the date populated in --DTC for the observation, --STDTC is the relative day of the date populated in --STDTC for the observation; and --ENDY is the relative day of the of the date populated in --ENDTC for the observation. All relative 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
2	Days Relative to Other Applicant-Defined Reference Dates	Applicants may represent days relative to other applicant-defined reference dates beyond a reference period for a study. In such cases: Relative days will be represented in a nonstandard variable (NSV) in a --SUPP dataset associated with the domain. All relative day values will be integers and there will be no day 0. The reference date is considered day 1 and the relative day value is increased by 1 for each date following the reference date and decreased by 1 for each date prior to the reference date.
3	Timing Relative to the Reference Start Date	Variable --STRF represents the timing of observations relative to an applicant-defined reference period represented in RFSTDTC and RFENDTC, when relative timing such as "BEFORE", "PRIOR", "ONGOING"', or "CONTINUING" is collected instead of a date and is collected in relation to the applicant-defined study reference period. --STRF is used to identify the start of an observation relative to the sponsor-defined study reference period. Allowable values for --STRF are "BEFORE", "DURING", "DURING/AFTER", "AFTER", and "UNKNOWN". Although "COINCIDENT" and "ONGOING" are in the STENRF codelist, they describe timing relative to a point in time rather than an interval of time, so are not appropriate for use with --STRF variables. It would be unusual for an event or intervention to be recorded as starting "AFTER" the study reference period, but could be possible, depending on how the study reference period is defined in a particular study.
4	Timing Relative to the Reference End Date	Variable --STRF represents the timing of observations relative to an applicant-defined reference period represented in RFSTDTC and RFENDTC, when relative timing such as "BEFORE", "PRIOR", "ONGOING"', or "CONTINUING" is collected instead of a date and is collected in relation to the applicant-defined study reference period. --ENRF is used to identify the end of an observation relative to the sponsor-defined study reference period. Allowable values for --ENRF are "BEFORE", "DURING", "DURING/AFTER", "AFTER" and "UNKNOWN". If --ENRF is used, then --ENRF = "AFTER" means that the event did not end before or during the study reference period. Although "COINCIDENT" and "ONGOING" are in the STENRF codelist, they describe timing relative to a point in time rather than an interval of time, so are not appropriate for use with --ENRF variables.


	--STRTPT, --STTPT, --ENRTPT, and --ENTPT	Although the variables --STRF and --ENRF are useful in the case when relative timing assessments are made coincident with the start and end of the study reference period, they may not be suitable for expressing relative timing assessments (e.g., "Prior", "Ongoing") that are collected at other times of the study. As a result, 4 new timing variables were added in SDTMIG v3.1.2 to express a similar concept at any point in time. The variables --STRTPT and --ENRTPT contain values similar to --STRF and --ENRF, but may be anchored with any timing description or date/time value expressed in the respective --STTPT and --ENTPT variables, and are not limited to the study reference period. Unlike the variables --STRF and --ENRF, which for all domains are defined relative to one study reference period, the timing variables --STRTPT, --STTPT, --ENRTPT, and --ENTPT are defined by each sponsor for each study. Allowable values for --STRTPT and --ENRTPT are as follows. If the reference time point corresponds to the date of collection or assessment: Start values: An observation can start BEFORE that time point, can start COINCIDENT with that time point, or it can be UNKNOWN when it started. End values: An observation can end BEFORE that time point, can end COINCIDENT with that time point, can be known that it did not end but was ONGOING, or it can be UNKNOWN when it ended or if it was ongoing. AFTER is not a valid value in this case because it would represent an event after the date of collection. If the reference time point is prior to the date of collection or assessment: Start values: An observation can start BEFORE the reference point, can start COINCIDENT with the reference point, can start AFTER the reference point, or it can be UNKNOWN when it started. End values: An observation can end BEFORE the reference point, can end COINCIDENT with the reference point, can end AFTER the reference point, can be known that it did not end but was ONGOING, or it can be UNKNOWN when it ended or if it was ongoing. Although "DURING" and "DURING/AFTER" are in the STENRF codelist, they describe timing relative to an interval of time rather than a point in time, so are not allowable for use with --STRTPT and --ENRTPT variables.

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Representing References and Relative Timing