The HCUP data element for the hospital's ownership/control category has changed over time. In the 1988-1992 NIS, the hospital's ownership/control category was stored in the variable ST_OWNER. In the 1993-1997 NIS, this same information is stored in the variable H_CONTRL. Beginning with the 1998 NIS, the name HOSP_CONTROL is used.

Although the categories for hospital control do not change across years, the labels used to describe hospitals do change:

• Government, nonfederal is equivalent to public
• Private not-for-profit is equivalent to voluntary
• Private investor-owned/private for profit is equivalent to proprietary.

Hospitals in different ownership/control categories tend to have different missions and different responses to government regulations and policies.

The hospital's ownership/control category was obtained from the AHA Annual Survey of Hospitals.

Hospital ownership (ST_OWNER) 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.