Bedsize categories are based on hospital beds, and are specific to the hospital's location and teaching status. Bedsize assesses the number of short-term acute care beds set up and staffed in a hospital. Hospital information was obtained from the AHA Annual Survey of Hospitals.

Beginning in 1998, the hospital's bedsize categories are defined using region of the U.S., the urban-rural designation of the hospital, in addition to the teaching status.

• Rural hospitals were not split according to teaching status, because rural teaching hospitals were rare. Prior to 2004 data, the urban/rural designation was based on Metropolitan Statistical Areas (MSA). Beginning with the 2004 data, this designation was determined by the Core Based Statistical Area (CBSA). This change in 2004 contributed to a slight decline in the number of hospitals that were classified as rural and a corresponding increase in the number of hospitals that were classified as urban.
• A hospital is considered a teaching hospital if it has one or more Accreditation Council for Graduate Medical Education (ACGME) approved residency programs, is a member of the Council of Teaching Hospitals (COTH) or has a ratio of full-time equivalent interns and residents to beds of .25 or higher. Beginning with the 2014 NIS, there is an increase in the number of hospitals identified as teaching facilities because the AHA Annual Survey showed an increase in facilities with approved residency programs. About this time, the ACGME became the primary organization for residency training approval.

Prior to 1988, the bedsize category did not vary by region and teaching hospitals were defined as having an AMA approved residency program or having membership in the Council of Teaching Hospitals.

In the 1988-1992 NIS, the hospital's bedsize category was stored in the variable ST_BEDSZ. In the 1993-1997 NIS, this same information is stored in the variable H_BEDSZ. Beginning with the 1998 NIS, the name HOSP_BEDSIZE is used.

For detailed information about the NIS sampling design, see the year-specific report on the Design of the HCUP Nationwide Inpatient Sample.

In the NIS prior to 2012, HOSP_BEDSIZE is missing if the data source that contributed discharge data to the NIS prohibits the release of hospital identifiers.