The hospital's ownership/control category was obtained from the AHA Annual Survey of Hospitals and includes categories for government nonfederal (public), private not-for-profit (voluntary) and private investor-owned (proprietary). These types of hospitals tend to have different missions and different responses to government regulations and policies.

When the sample size was sufficiently large, hospitals were stratified as public (HOSP_CONTROL=1), voluntary (HOSP_CONTROL=2), and proprietary (HOSP_CONTROL=3). This stratification was used for Southern rural, Southern urban nonteaching, and Western urban nonteaching hospitals. For smaller strata - the Midwestern rural and Western rural hospitals - a collapsed stratification of public versus private was used, with the voluntary and proprietary hospitals combined to form a single "private" category (HOSP_CONTROL=4). For all other combinations of region, location and teaching status, no stratification based on control was advisable given the number of hospitals in these cells (HOSP_CONTROL=0).

The HCUP variable name 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.

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

HOSP_CONTROL is missing if the data source that contributed discharge data to the NIS prohibits the release of hospital identifiers.