OBSERVATION_PERIOD represents the spans of time for which a person is
at-risk to have clinical events recorded within the source systems, even if
no events in fact are recorded (healthy patient with no healthcare
interactions).
http://www.ohdsi.org/web/wiki/doku.php?id=documentation:cdm:observation_period
Some observational data sources have this information explicitly available
in the source data. For example, many payers have insurance claims data
where the beneficiary enrollment records define the periods of time when
you should see data (because its the time when a person can submit claims
for reimbursement).
Other systems do not have this explicit, so the observation periods need to
be inferred. For example, some sources that contain electronic health
records have inferred the observation period as the duration from the first
observation date to the last observation date. Other sources have tried to
define the spans of time when you have confidence in observing data.
There’s been a couple threads on this topic before, you can search for
others in the forums, but one that you may find useful is here:
.