The HCUP variable for the hospital's location and teaching status changed names and definitions across data years:

For LOCTEACH, the hospital's location and teaching status were obtained from the AHA Annual Survey of Hospitals. A metropolitan statistical area is considered urban, and a non-metropolitan statistical area is rural. Teaching hospitals have an AMA-approved residency program or have membership in the Council of Teaching Hospitals.

Note that a few hospitals classified as rural are also teaching hospitals.

The hospital location and teaching status (LOCTEACH) is missing for some zero-weight hospitals for which the information was not available (see the File Composition for the Nationwide Inpatient Sample for a definition of zero-weight hospitals). Zero-weight hospitals are included in the 1988-1992 data for NIS, Release 1. Because relatively few hospitals were affected and the complexity of including these hospitals entailed considerable processing burden and costs, no zero-weight hospitals are included in the NIS after 1992.