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 procedures, and charges for all patients regardless of payer.
The 2008 HCUP (NIS) includes all discharge data from 1,056 hospitals in 42 states. This sample of hospitals represents approximately 90% of U.S. community hospital discharges in the U.S. The number of states included in the NIS varies by year and has grown from 8 in the first year to 42 at present.
The 2008 HCUP (NIS) approximates a 20% stratified sample of U.S. community hospitals (nonfederal, short-term, general, and other specialty hospitals, excluding hospital units of institutions). This universe of community hospitals is divided into strata using five hospital characteristics: ownership or control, bed size, teaching status, urban or rural location, and U.S. region. The NIS is a stratified probability sample of hospitals in the frame, with sampling probabilities proportional to the number of U.S. community hospitals in each strata. 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 2006 HCUP (NIS) contains data from approximately 8 million hospital stays from roughly 1,000 hospitals. The Inpatient Core file contains data for 100% of the discharges from a sample of hospitals in participating states.
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.