Agency for Healthcare Research and Quality (AHRQ)
1988 to present
The Healthcare Cost and Utilization Project (HCUP) is a family of health care databases and related software tools developed through a federal-state-industry partnership to build a multistate health data system for health care research and decision making. The National (Nationwide) Inpatient Sample (NIS), a component of HCUP, is the largest all-payer inpatient care database that is publicly available in the U.S. Beginning with 2012 data year, the NIS was redesigned. It approximates a 20-percent stratified sample of all discharges from US community hospitals, excluding rehabilitation and long-term acute care hospitals. Weights are provided to trend across the two different designs.
The HCUP NIS contains a core set of clinical and nonclinical information found in a typical discharge abstract, including all-listed diagnoses and procedures, discharge status, patient demographics, and charges for all patients regardless of payer (including discharges that are self-pay, no charge, charity or no payment is expected).
The 2016 HCUP NIS includes all discharge data from 4,573 hospitals. This 2016 NIS sampling frame is comprised of 46 states and the District of Columbia, covering more than 97% of the US population and includes almost 96% of dischargers in the US community hospitals. The number of states included in the NIS varies by year and has grown from 8 in the first year to 47 (including the District of Columbia) at present.
The 2016 HCUP (NIS) approximates a 20% stratified sample of all discharges from U.S. community hospitals (nonfederal, short-term, general, and other specialty hospitals, excluding hospital units of institutions). The systematic sampling starting in 2012 is a self-weighted sample design similar to simple sample random sampling. It ensures that the sample is representative of the population on the following critical factors: census division of the hospital, hospital ownership, urban-rural location of the hospital, hospital teaching status, number of beds in the hospital, diagnosis-related group for the hospital stay, and admission month of the hospital stay. The frame is limited by the availability of inpatient data from the data sources currently participating in HCUP. The information abstracted from hospital discharge records is translated into a uniform format to facilitate both multistate and national-state comparisons and analyses.
Response Rates and Sample Size
The 2016 HCUP NIS contains data from approximately 8 million hospital stays from roughly 4,500 hospitals.
Periodically, new data elements are added to the NIS and some are dropped. Although weights are produced to create estimates that approximate a nationally representative sample, because not all states provide data, some bias in national estimates may occur if omitted states have substantially different hospitalization patterns than states that provided data. The number of states in the HCUP (NIS) varies by year.
Agency for Healthcare Research and Quality (AHRQ), Healthcare Cost and Utilization Project (HCUP), Overview of National Inpatient Sample (NIS)