Good point. Currently, the (unspoken) convention is this: Beyond person_id and date (datetime) no two medical events have mandatory and explicit links. Because most data sources don't care providing them. We have a whole lot of Analytics, which attempt to link things implicitly, like through cohort definitions and estimations. The reason we have visits, again unspoken, is to determine which kind of healthcare interaction was had during some clinical event, and to draw two types of conclusions: Severity of a Condition (ER and hospital are bad) and, much less common if your name is not @Mark_Danese, effectiveness of the healthcare organization: cost, location, specialty, etc.
If you want a "central join table" you'd have to explain what that means and what the analytical use case would be.
Yes, we could. But we cannot. Because the data are notoriously bad providing this information, even though you'd think it'd be pretty central to what happens to those patients. The reason is that the primary use of the data is for managing the healthcare organization or payment for healthcare, not for capturing the patient experience. Even medical charting should play a big role in the EHRs: A big chunk of what's in the raw Cerner/EPIC/Allscripts etc. is about scheduling, ordering, billing and communication between providers. Claims data are not better: they are organized around how the organizations want to get their money, not how the patients got diagnosed and treated.
Making a field in the OMOP CDM mandatory will not change that. All you get is a bunch of NULLs or 0s.
Well, that alone is of questionable value, but even if you want to create those zombie visits - you need to have the information what belongs to a Visit, and cobbling it together from VISIT_DETAIL we know can be a crap-shoot.
Yes, but if you abolish the direct link from the event tables you force VISIT_DETAIL to be a carbon copy of those. Each time a psych counsel or radiological report comes in you'd force a new VISIT_DETAIL record. That was not the idea of that table.
@Gowtham_Rao: I have a lot of sympathy for what you are trying to do, but making visit_occurrence_id mandatory will not solve the problem. It's like a prohibition law.
On the other hand, allowing for pharmacy visit records is totally fine and supported by the current model. A pharmacy visit (derived from a pharmacy claim) would be independent from the doctor's visit (from a medical claim), and care_site and location will tell you which pharmacy the patient went to. In EHR records, we won't have these. So, what's the problem?