The results presented in this report are drawn from the Healthcare Cost and Utilization Project (HCUP), a Federal-State-Industry partnership to build a multi-State health care data system. This partnership is sponsored by the Agency for Healthcare Research and Quality (AHRQ) and is managed by staff in AHRQ's Center for Delivery, Organization, and Markets (CDOM). HCUP is based on data collected by individual State Partner organizations (including State departments of health, hospital associations, and private agencies), which provide the data to AHRQ. HCUP would not be possible without statewide data collection projects and their partnership with AHRQ.
For the year 2002, 36 State Partner organizations contributed their data to AHRQ, where all files were validated and converted into a uniform format. The uniform HCUP databases enable comparative studies of health care services and the use and cost of hospital care, including:
HCUP includes short-term, non-Federal, community hospitals as defined by the American Hospital Association (AHA). This definition includes general hospitals and specialty facilities, such as pediatric, obstetrics-gynecology, short-term rehabilitation, and oncology hospitals. Long-term care and psychiatric hospitals are excluded, as are substance abuse treatment facilities.
HCUP includes several sets of inpatient databases for health services research. This report is based on the 2002 Nationwide Inpatient Sample (NIS) data. The NIS is the largest all-payer inpatient care database that is publicly available in the U.S. The database contains data for more than 7 million hospital stays from roughly 1,000 hospitals sampled to approximate a 20-percent stratified sample of U.S. community hospitals. The data are weighted to obtain estimates representing the total number of inpatient hospital discharges in the U.S.; in the year 2002, this figure was approximately 37.8 million.
This report is based on data within the Healthcare Cost and Utilization Project (HCUP) Nationwide Inpatient Sample (NIS) database. The NIS data are weighted to obtain estimates representing the total number of inpatient hospital discharges in the U.S.; in 2002, this figure totaled 37,804,021 and in 1997, there were 34,680,628 estimated discharges. The 2002 NIS was based on a sampling frame of 35 states, compared with 22 states in the 1997 NIS. A brief discussion of selected methodological issues pertaining to this Fact Book follows.
Clinical diagnoses are recorded within the NIS using the International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM). While ICD-9-CM codes may be used to provide descriptive statistics, the granular nature of ICD-9-CM reporting is difficult to summarize. Thus, for this report, the AHRQ-developed Clinical Classifications Software (CCS) is applied to hospital records to aggregate ICD-9-CM diagnosis and procedure codes into a limited number of clinically-meaningful categories for most tables. Major Diagnostic Categories and Diagnosis Related Groups are also used for some analyses. More detailed information on CCS can be downloaded from the HCUP User Support Web site at: http://www.hcup-us.ahrq.gov/home.jsp.
For this report, the unit of analysis is the inpatient stay rather than the patient. For example, a patient admitted four times to the hospital is included four times in the NIS data. Thus, the same individual can account for more than one hospital stay. Frequencies and rankings of diagnoses are based on principal, or first-listed, diagnosis, which is defined as the main reason for the hospital stay after evaluation.
Payer is the expected payer for the hospital stay. To make coding uniform across all HCUP data sources, "Payer" combines detailed categories into more general groups:
Up to two payers can be coded for a hospital stay in HCUP data. When this occurs, the following hierarchy was used:
Data indicating "total hospital charges" are the amount the hospital billed for the entire hospital stay. These charges do not necessarily reflect reimbursements or costs and do not include most professional (physician) fees. Typically, charges are higher than actual costs. Costs are calculated from charges using cost-to-charge ratios based on data from Medicare Cost Reports. Costs represent the resource costs to produce services plus an additional allowance for bad debt (approximately 5 percent) and ordinary net income (approximately 3 percent), based on the long-run average for the industry.
Aggregate charges, or the "national bill," is the sum of all charges for all hospital stays in the U.S. When a case is missing information on charges, a value is imputed by taking the mean charges for all discharges of the same DRG with non-missing charges. Fewer than 7.5 percent of cases are missing charge data in HCUP data. Because of the way in which missing charges are imputed, simple calculation of the number of discharges multiplied by the mean charge will not always equal aggregate charges.
Because this Fact Book updates an earlier report that depicted hospital care in 1997, this document provides many comparative statistics that reflect how hospital care has evolved from 1997 to 2002. Only statistically significant differences (p-value <= .05) are presented.
1 U.S. Census Bureau, Population Division. National population estimates—Characteristics: Annual estimates of the population by sex and selected age groups for the United States: April 1, 2000 to July 1, 2003. http://www.census.gov/popest/national/asrh/NC-EST2003-as.html (Accessed March 7, 2005).
2 Mills RJ, Bhandari S. Health insurance coverage in the United States: 2002. Current Population Reports P60-223. Washington, DC: U.S. Census Bureau, September 2003. http://www.census.gov/prod/2003pubs/p60-223.pdf (Accessed March 7, 2005).
3 American Hospital Association. Hospital Statistics, 2004. Chicago: Health Forum, 2004.
4 U.S. Census Bureau, Population Division. National intercensal estimates (1990-2000). http://www.census.gov/popest/archives/est90intercensal/us-est90int-01.html (Accessed March 8, 2005).
5 Elixhauser A, Steiner C, Harris DR, Coffey RM. Comorbidity measures for use with administrative data. Medical Care 1998; 36(1):8-27.
6 Cardenas E. Revision of the CPI hospital services component. [Excerpt]. Monthly Labor Review Online 1996; 119(12). http://www.bls.gov/opub/mlr/1996/12/art6exc.htm (Accessed March 7, 2005).
7 Bennefield R. Health insurance coverage: 1997. Current Population Reports, P60-202. Washington, DC: U.S. Census Bureau, September 1998. http://www.census.gov/prod/3/98pubs/p60-202.pdf (Accessed March 8, 2005).
More information regarding HCUP data is available at http://www.ahrq.gov/data/hcup, as well as on the HCUP User Support Web site at http://www.hcup-us.ahrq.gov.
Additional descriptive statistics can be viewed through HCUPnet (http://hcupnet.ahrq.gov/), a Web-based tool providing easy access to information on hospital stays.
NIS data are available for the following data years:
NIS data can be purchased for research through the HCUP Central Distributor sponsored by AHRQ: Social and Scientific Systems, Inc., phone: 866-556-4287 (toll-free), fax: 301-628-3201, or E-mail: hcup@s-3.com.
Price of the data is $322 for Release 1; $160 per year for 1993 to 1999; and $200 per year for 2000 to 2003. All prices may be higher for customers outside the U.S., Canada, and Mexico.
AHRQ is always looking for ways in which AHRQ-funded research, products, and tools have influenced clinical practice, improved policies, affected patient outcomes, and changed people's lives. Impact case studies describe AHRQ research findings in action. These case studies have been used in testimony, budget documents, and speeches. If you are aware of any impact your research has had on health care policy, clinical practice, or patient outcomes, please let us know by using the contact information below.
Healthcare Cost and Utilization Project (HCUP)
Center for Delivery, Organization, and Markets
Agency for Healthcare Research and Quality
Phone: 866-290-HCUP (4287)
E-mail: hcup@ahrq.gov
Previously published HCUP Fact Books are available from the AHRQ Publications Clearinghouse. To order by telephone, please call 800-358-9295 with the title and publication number; or request a copy via E-mail at AHRQPubs@ahrq.hhs.gov.