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. HOSP_CONTROL is used as a stratifier for the HCUP nationwide databases: Nationwide Inpatient Sample (NIS), Kids' Inpatient Database (KID), and Nationwide Emergency Department Sample (NEDS).

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).