I don’t favor dropping either because we face a situation with drug dispensing data in the nursing home setting where the source data provides a prescription end date that has a different meaning then what can be inferred from days supply. If the drug_exposure table is supposed to closely match the source orders, dropping either field would cause a loss of information for our use case.
Specifically, because patients tend to reside in the home for long periods of time, it is often the case that an order is started with no stop date but with a days supply. The clinician later places a “stop order” indicating the date that the order should be stopped. There are no records of refill orders or holds (which occur frequently because of transfers to and from the hospital). Rather, as long as the Rx is active, dispensing continues. To calculate accurate drug_eras (ones that closely match actual administration), we have to consider both the end date (if available) and days supply fields in addition to other information about the patient’s actual time in the facility. For some kinds of studies, such detail might be avoided but we are working on patient predictive models where we think it matters.