The Nationwide Inpatient Sample (NIS) is the largest all-payer inpatient care database in the United States. The NIS is a publicly available database that contains information on hospital inpatient stays from over 1,000 hospitals in more than 45 states. It is maintained by the Agency for Healthcare Research and Quality (AHRQ) and is widely used by researchers, policymakers, and healthcare professionals to analyze trends in healthcare utilization, outcomes, and costs. The NIS includes data on patient demographics, diagnoses, procedures, and hospital characteristics, making it a valuable resource for studying a wide range of healthcare issues.