Hi @Akshay,
Re:
Start with the definition of the table: uniquely define 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).
The Observation Period is dependent on your data. For EHR data, many data holders believe their Observation Period starts with the first date a Person has an interaction* with their healthcare system and ends with the date of the data extraction. This logic assumes a Person would return to their institution if they required care. See the discussion here. However, your logic may differ from the above depending on the way data is recorded in your EHR.
*Depending on your particular EHR instance, an “interaction” may be defined as a Visit, if a Visit is always the first interaction in your health system. Colorado defines “interaction” as any clinical event since pre-visit activities generate data in our EHR.
It’s not possible. Electricity was sparse in 1899 and there definitely wasn’t any EHR system in use.
I suggest you take a close look at those records. Is this a problem with the Observation Period? Or is this a problem with the data? Many EHR systems use default dates instead of leaving certain dates NULL. Birthdates in 1850 or drug dispenses Jan. 1, 1970.