Procedures in U.S. Hospitals, 2003: HCUP Fact Book No. 7 (continued)

Source of Data for This Report

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 2003, 38 State Partner organizations contributed their data to AHRQ, where all files are 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:

• Effects of market forces on hospitals and the care they provide.
• Variations in medical practice.
• Effectiveness of medical technology and treatments.
• Use of services by special populations.

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 2003 Nationwide Inpatient Sample (NIS) data, which includes data from 37 of our participating Partners that supplied 2003 data to the project. The NIS is the largest all-payer inpatient care database that is publicly available in the U.S. The database contains data for nearly 8 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 United States; in the year 2003, this figure is approximately 38 million.

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Methods

This report is based on data from the HCUP Nationwide Inpatient Sample database. The NIS data are weighted to obtain estimates representing the total number of inpatient hospital discharges in the United States; in 2003, this figure totaled 38,220,659. The 2003 NIS is based on a sampling frame of 37 States compared with 22 States in the 1997 NIS. A brief discussion of selected methodological issues pertaining to this Fact Book follows.

Diagnoses and Clinical Classification Software (CCS)

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. More detailed information on CCS can be downloaded from the HCUP User Support Web site at: http://www.hcup-us.ahrq.gov/home.jsp.

Procedure Classes

The Procedure Classes tool provides an easy way to categorize ICD-9-CM procedure codes into one of four broad categories: minor diagnostic, minor therapeutic, major diagnostic, and major therapeutic. This tool was created to facilitate health services research on hospital procedures using administrative data. All ICD-9-CM procedure codes are assigned to one of the following categories:

1. Minor diagnostic—Non-operating room procedures that are diagnostic (e.g., 87.03 CT scan of head).
2. Minor therapeutic—Non-operating room procedures that are therapeutic (e.g., 02.41 Irrigate ventricular shunt).
3. Major diagnostic—All procedures considered valid operating room procedures by the DRG grouper and that are performed for diagnostic reasons (e.g., 01.14 Open brain biopsy).
4. Major therapeutic—All procedures considered valid operating room procedures by the DRG grouper and that are performed for therapeutic reasons (e.g., 39.24 Aorta-renal bypass).

More detailed information on the Procedure Classes tool can be obtained from the HCUP User Support Web site at: http://www.hcup-us.ahrq.gov/toolssoftware/procedure/procedure.jsp.

Unit of Analysis

For this report, the unit of analysis is the inpatient stay rather than the patient or the procedure. For example, a patient admitted 4 times to the hospital is included 4 times in the NIS data. Thus, the same individual can account for more than 1 hospital stay. Also, frequencies and rankings of procedures are based on all-listed procedures codes on a discharge record—and are not limited to the principal procedure code. Each HCUP NIS record can contain up to 15 procedure codes. This Fact Book provides information on all procedures performed during the stay. The unit of analysis remains the discharge: if a particular CCS procedure code occurs multiple times during the same discharge, it is still counted only once.

Definition of Payer

Payer is the expected payer for the hospital stay. It is important to note that charges billed to payers reflect the entire hospital stay, not a charge for a specific procedure. To make coding uniform across all HCUP data sources, the payer variable combines detailed categories into more general groups:

• Medicare includes fee-for-service and managed care Medicare patients.
• Medicaid includes fee-for-service and managed care Medicaid patients.
• Private insurance includes Blue Cross, commercial carriers, and private HMOs and PPOs.
• Uninsured includes an insurance status of "self-pay" and "no charge."
• Other includes Workers' Compensation, CHAMPUS, CHAMPVA, Title V, and other government programs.

Up to two payers can be coded for a hospital stay in HCUP data. When this occurs, the following hierarchy is used:

• If either payer is listed as Medicaid—payer is "Medicaid."
• For non-Medicaid stays, if either payer is listed as Medicare—payer is "Medicare."
• For stays that are neither Medicaid nor Medicare, if either payer is listed as private insurance—payer is "private insurance."
• For stays that are not Medicaid, Medicare, or private insurance, if either payer is some other third party payer—payer is "other."
• For stays that have no third-party payer and the payer is listed as "self-pay" or "no charge"—payer is "uninsured."
• If no insurance information is available—payer is missing.

Charges

Data indicating "hospital charges" are the amount the hospital billed for the entire hospital stay—not for a specific procedure. These charges do not necessarily reflect reimbursements or costs and do not include professional (physician) fees. Typically, charges are higher than actual costs.

High-Volume Providers

High-Volume Providers Research indicates that hospitals that perform more than a specific number of certain procedures have fewer in-hospital deaths for those particular procedures than lower volume hospitals. This "threshold number" varies with the type of procedure. The volume thresholds used in this Fact Book are adapted from Dudley, et al.¹:

New Weights for 1997 NIS Data

In 1998, the NIS sample design was changed:

• Rehabilitation hospitals were excluded from the NIS hospital universe and sample.
• AHA hospital unit discharges were used instead of total facility discharges, which include nursing home unit discharges.

In order to facilitate analysis of trends using multiple years of NIS data, alternate weights for NIS discharge and hospital data for the 1988-1997 HCUP NIS were developed. These alternative weights were calculated in the same way as the weights for the 1998 and later years of the NIS. These new weights were applied to the 1997 data presented in this report. The NIS Trends Report includes details regarding the alternate weights and other recommendations for trends analysis: http://www.hcup-us.ahrq.gov/reports/TrendReport2005_1.pdf (PDF Help). The new weights are available at: http://www.hcup-us.ahrq.gov/db/nation/nis/trendwghts.jsp.

Comparisons of 1997 and 2003 Hospital Procedures

Because this Fact Book updates an earlier report that described hospital procedures in 1997, this document provides many comparative statistics that reflect how hospital care has evolved from 1997 to 2003. Only statistically significant differences (p-value < or = .05) are presented.

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References

1. Dudley RA, Johansen KL, Brand R, Rennie DJ,Milstein A. Selective referral to high-volume hospitals: estimating potentially avoidable deaths. JAMA 2000 Mar 1;283(9):1159-66. http://www.census.gov/popest/national/asrh/NC-EST2003-as.html (Accessed March 7, 2005).

2. DeNavas-Walt C, Proctor BD, Mills RJ. Income, poverty, and health insurance coverage in the United States: 2003. Current population reports P60-226. Washington, DC: U.S. Census Bureau; August 2004. http://www.census.gov/prod/2004pubs/p60-226.pdf. (Accessed November 12, 2005).

3. American Hospital Association. Fast facts on U.S. hospitals from AHA hospital statistics. http://www.aha.org/aha/resource_center/fastfacts/fast_facts_U.S._hospitals.html. (Accessed November 1, 2005).

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. 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 November 10, 2005).

6. U.S. Department of Labor. Bureau of Labor Statistics. Producer price indexes. http://www.bls.gov/ppi/home.htm. (Accessed November 10, 2005).

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For More Information

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://hcup.ahrq.gov/hcupnet.asp), a Web-based tool providing easy access to information on hospital stays.

NIS data are available for the following data years:

• 2003 data (available June 2005).
• 2002 data.
• 2001 data.
• 2000 data.
• 1999 data (PB 2002-500020).
• 1998 data (PB 2001-500092).
• 1997 data, Release 6 (PB 2000-500006).
• 1996 data, Release 5 (PB 99-500480).
• 1995 data, Release 4 (PB 98-500440).
• 1994 data, Release 3 (PB 97-500433).
• 1993 data, Release 2 (PB 96-501325).
• 1988-1992 data, Release 1 (PB 95-503710).

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

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Acknowledgments

Thanks to the following individuals for their collaboration in producing this Fact Book: David Ross (Thomson Medstat) and Julie Nisbet (Thomson Medstat) for statistical programming, Megan Mulligan (Thomson Medstat) for administrative support, Gail Eisen (Thomson Medstat) and DonnaRae Castillo (AHRQ) for editorial guidance, and The Madison Design Group (MDG) for design and layout assistance.

AHRQ Publication No. 06-0039
Current as of May 2006

Internet Citation:

Merrill CT, Elixhauser A. Procedures in U.S. Hospitals, 2003: HCUP Fact Book No. 7. AHRQ Publication No. 06-0039, May 2006. Agency for Healthcare Research and Quality, Rockville, MD. http://www.ahrq.gov/data/hcup/factbk7/

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