Representing References and Relative Timing

Variables --DY, --STDY, and --ENDY represent 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

Applicants may represent days relative to applicant-defined reference dates. In such cases:

• Values will be integers.
• The reference date will be day 1.
• Relative days will be represented in a nonstandard variable (NSV) in a --SUPP dataset associated with the domain. 

The variables --STRF and --ENRF represent the timing of an observation relative to the sponsor-defined study reference period, when information such as "BEFORE", "PRIOR", "ONGOING"', or "CONTINUING" is collected in lieu of a date and this collected information is in relation to the sponsor-defined study reference period. The sponsor-defined study reference period is the continuous period of time defined by the discrete starting point, RFSTDTC, and the discrete ending point, RFENDTC, for each subject in the Demographics (DM) dataset.

--STRF is used to identify the start of an observation relative to the sponsor-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 --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.

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.
As an example, a CRF checkbox that identifies concomitant medication use that began prior to the study reference period would translate into CMSTRF = "BEFORE", if selected. Note that in this example, the information collected is with respect to the start of the concomitant medication use only, and therefore the collected data corresponds to variable CMSTRF, not CMENRF. Note also that the information collected is relative to the study reference period, which meets the definition of CMSTRF.

Some sponsors may wish to derive --STRF and --ENRF for analysis or reporting purposes even when dates are collected. Sponsors are cautioned that doing so in conjunction with directly collecting or mapping data such as "BEFORE", "PRIOR", and "ONGOING" to --STRF and --ENRF will blur the distinction between collected and derived values within the domain. Sponsors wishing to do such derivations are instead encouraged to use analysis datasets for this derived data.

In general, sponsors are cautioned that representing information using variables --STRF and --ENRF may not be as precise as other methods, particularly because information is often collected relative to a point in time or to a period of time other than the one defined as the study reference period. SDTMIG v3.1.2 attempted to address these limitations by the addition of 4 new relative timing variables, which are described in the following section. Sponsors should use the set of variables that allows for accurate representation of collected data. In many cases, this will mean using these new relative timing variables in place of --STRF and --ENRF.

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.