Update days_supply description and convention

inst/csv/OMOP_CDMv5.4_Field_Level.csv

@@ -100,7 +100,7 @@ drug_exposure,refills,No,integer,This is only filled in when the record is comin
 drug_exposure,quantity,No,float,NA,"To find the dose form of a drug the RELATIONSHIP table can be used where the relationship_id is 'Has dose form'. If liquid, quantity stands for the total amount dispensed or ordered of ingredient in the units given by the drug_strength table. If the unit from the source data does not align with the unit in the DRUG_STRENGTH table the quantity should be converted to the correct unit given in DRUG_STRENGTH. For clinical drugs with fixed dose forms (tablets etc.) the quantity is the number of units/tablets/capsules prescribed or dispensed (can be partial, but then only 1/2 or 1/3, not 0.01). Clinical drugs with divisible dose forms (injections) the quantity is the amount of ingredient the patient got. For example, if the injection is 2mg/mL but the patient got 80mL then quantity is reported as 160.
 Quantified clinical drugs with divisible dose forms (prefilled syringes), the quantity is the amount of ingredient similar to clinical drugs. Please see [how to calculate drug dose](https://ohdsi.github.io/CommonDataModel/drug_dose.html) for more information.
 ",No,No,NA,NA,NA,NA,NA
-drug_exposure,days_supply,No,integer,NA,Days supply of the drug. This should be the verbatim days_supply as given on the prescription. If the drug is physician administered use duration end date if given or set to 1 as default if duration is not available.,No,No,NA,NA,NA,NA,NA
+drug_exposure,days_supply,No,integer,"The number of days of supply of the medication as recorded in the original prescription or dispensing record. Days supply can differ from actual drug duration (i.e. prescribed days supply vs actual exposure).","The field should be left empty if the source data does not contain a verbatim days_supply, and should not be calculated from other fields.Negative values are not allowed. Several actions are possible: 1) record is not trustworthy and we remove the record entirely. 2) we trust the record and leave days_supply empty or 3) record needs to be combined with other record (e.g. reversal of prescription). High values (>365 days) should be investigated. If considered an error in the source data (e.g. typo), the value needs to be excluded to prevent creation of unrealistic long eras.",No,No,NA,NA,NA,NA,NA
 drug_exposure,sig,No,varchar(MAX),This is the verbatim instruction for the drug as written by the provider.,"Put the written out instructions for the drug as it is verbatim in the source, if available.",No,No,NA,NA,NA,NA,NA
 drug_exposure,route_concept_id,No,integer,NA,The standard CONCEPT_ID that the ROUTE_SOURCE_VALUE maps to in the route domain.,No,Yes,CONCEPT,CONCEPT_ID,Route,NA,NA
 drug_exposure,lot_number,No,varchar(50),NA,NA,No,No,NA,NA,NA,NA,NA