Added THEMIS issue #13 to VISIT_OCCURRENCE

Documentation/CommonDataModel_Wiki_Files/StandardizedClinicalDataTables/VISIT_OCCURRENCE.md

@@ -35,3 +35,4 @@ No.|Convention Description
 | 9  | Visits are recorded in various data sources in different forms with varying levels of standardization. For example:<br><ul><li>Medical Claims include Inpatient Admissions, Outpatient Services, and Emergency Room visits.</li><li>Electronic Health Records may capture Person visits as part of the activities recorded depending whether the EHR system is used at the different Care Sites./li></ul> |
 | 10 | In addition to the 'Place of Service' vocabulary the following SNOMED concepts for discharge disposition (DISCHARGE_TO_CONCEPT_ID) can be used:<br><ul><li>Patient died: 4216643</li><li>Absent without leave: 44814693</li><li>Patient self-discharge against medical advice: 4021968</li></ul> |
 | 11 | PRECEDING_VISIT_ID can be used to link a visit immediately preceding the current visit. |
+| 12 | Visit end dates are mandatory. If end dates are not provided in the source there are three ways in which to derive them:<br><ul><li>Outpatient Visit: VISIT_END_DATE = VISIT_START_DATE</li><li>Emergency Room Visit: VISIT_END_DATE = VISIT_START_DATE</li><li>Inpatient Visit: Usually there is information about discharge. If not, you should be able to derive the end date from the sudden decline of activity or from the absence of inpatient procedures/drugs.</li><li>Long Term Care Visits: Particularly for claims data, if end dates are not provided assume the visit is for the duration of month that it occurs.</li><li>For inpatient visits ongoing at the date of ETL, put date of processing the data as mandatory VISIT_END_DATE and VISIT_TYPE_CONCEPT_ID with 32220-"Still patient" to identify the visit as incomplete.</li></ul>([THEMIS issue #13](https://github.com/OHDSI/Themis/issues/13)).|