The NIS is the largest publicly available all-payer inpatient health care database in the United States, yielding national estimates of hospital inpatient stays. Unweighted, it contains data from more than 7 million hospital stays each year. Weighted, it estimates more than 36 million hospitalizations nationally. The NIS covers all patients, including individuals covered by Medicare, Medicaid, or private insurance, as well as those who are uninsured. It contains clinical and nonclinical data elements for each hospital stay, including:
• Primary and secondary diagnoses and procedures
• Patient demographic characteristics (e.g., sex, age, race, median household income for ZIP Code)
• Hospital characteristics (e.g., ownership)
• Expected payment source
• Total charges
• Discharge status
• Length of stay
