The HCUP variable name and definition for the hospital's teaching status has changed over time. In the 1993-1997 NIS, this information is stored in the variable H_TCH. Teaching status was obtained from the American Hospital Association (AHA) Annual Survey of hospitals. Teaching hospitals have an AMA-approved residency program or have a membership in the Council of Teaching Hospitals.

Beginning with the 1998 NIS, the name HOSP_TEACH is used and the definition of teaching hospitals was expanded to include hospitals with a ratio of .25 or higher of full-time equivalent interns and residents to non-nursing home beds.