 The HCUP is a Federal-State-Industry partnership providing all discharge data from 994 hospitals—approximately 8 million hospital stays each year.The Nationwide Inpatient Sample is the largest all-payer inpatient care database in the United States from which national estimates of inpatient care can be derived.Using safety data from the NIS, the AHRQ has been able to provide complication rates and risk data, even for rare surgical procedures, such as bariatric surgery.