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For some studies, a timeframe (the study reference period) study reference period, study reference points, and/or milestones may be defined per protocol, company policy, standard operating procedures, or other documented procedures. In such cases, the dates (and times when applicable) of the start and end of the study reference period, study reference points, and/or milestones will be collected.

When there is a need to need  Additionally, there may also be a need to collect information about whether an observation of interest occurred prior to a study reference point or milestone other than the beginning of the study reference period or was ongoing or ori continuing at some study reference point or milestone other than the end of the defined study reference period. In such cases, the dates (and times as applicable) of the start and end of the study reference period and/or study reference points or milestones will be collected. 

Relative timing variables are sets of CDASH Model variables that provide information about how the timing of the collected observation relates to either the study reference period or another study reference point or milestone.

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.

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