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For some studies, a timeframe (the study reference period) may be defined per protocol, company policy, standard operating procedures, or other documented procedures. Additionally, there may also be a need to collect information about whether an observation of interest occurred prior to a reference point or milestone other than the beginning of the study reference period or was ongoing or continuing at some reference point or milestone in the study other than the end of the defined study reference period.

Relative timing variables are sets of variables that provide information about how the timing of the collected observation relates to either the study reference period or another fixed point in time. CDASH relative timing variables are collected for observations where a date either is not collected or is not available. The CDASH set of variables serve as an indicator (or flag) that the observation's "start" was prior to the study reference period or prior to another fixed point in time OR that the observation's "end" was after or ongoing as of the study reference period or another fixed point in time. The CDASH variables of --PRIOR and --ONGO serve this purpose. How these collected flags are translated to tabulation datasets (according to controlled terminology) depends on whether the comparison is against the protocol-defined study reference period or against another fixed point in time serving as the "reference" for the timing of the record. To emphasize, collection of these CDASH relative timing variables is always dependent on the actual date either being prospectively not collected or not available.

For some studies, a timeframe (the study reference period) may be defined per protocol, company policy, standard operating procedures, or other documented procedures. The start and end dates of the study reference period are represented in tabulation variables RFSTDTC and RFENDTC.Regardless of how a study reference period is defined, the dates (and optionally times) of the start and end of that period can be collected.

If there is a need to collect information about whether an observation of interest occurred prior to a reference point or milestone other than the beginning of the study reference period or was ongoing or continuing at some reference point or milestone in the study other than the end of the defined study reference period, the date/time of that reference point or milestone should also be collected.

If there is a need to collect information about whether an observation of interest occurred prior to a reference point or milestone other than the beginning of the study reference period or was ongoing or continuing at some reference point or milestone in the study other than the end of the defined study reference period, the date/time of that reference point or milestone should also be collected. If this date/time has been collected, reasonable comparisons can be made to that date/time with “prior”, “coincident”, “continuing”, or “ongoing” questions.

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