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Introduction to the HCUP Nationwide Inpatient Sample (NIS), 2005
 

HEALTHCARE COST AND UTLIZATION PROJECT – HCUP
A FEDERAL-STATE-INDUSTRY PARTNERSHIP IN HEALTH DATA

Sponsored by the Agency for Healthcare Research and Quality

 

 

INTRODUCTION TO

THE HCUP NATIONWIDE INPATIENT SAMPLE (NIS),

2005

 

 

These pages provide only an introduction to the NIS package.

  For full documentation and notification of changes,
visit the HCUP User Support Website at http://www.hcup-us.ahrq.gov.

 

Issued June 2007

 

Agency for Healthcare Research and Quality
Healthcare Cost and Utilization Project (HCUP)
540 Gaither Road, 5th Floor
Rockville, Maryland 20850

Phone: (866) 290-HCUP (4287)
Fax: (301) 427- 1430
E-mail: hcup@ahrq.gov
Website: http://www.hcup-us.ahrq.gov

 

NIS Data and Documentation Distributed by:
HCUP Central Distributor

Phone: (866) 556-4287 (toll-free)
Fax: (866) 792-5313
E-mail: HCUPDistributor@ahrq.gov

Table of Contents

Index of Tables


HCUP NATIONWIDE INPATIENT SAMPLE ( NIS)
SUMMARY OF DATA USE LIMITATIONS

***** REMINDER *****


All users of the NIS must take the on-line Data Use Agreement (DUA) training session, sign a Data Use Agreement, and send a copy to AHRQ.

Authorized users of HCUP data agree to the following limitations: ‡

  • Will not use the data for any purpose other than research or aggregate statistical reporting.

  • Will not re-release any data to unauthorized users.

  • Will not identify or attempt to identify any individual.

  • Will not link HCUP data to data from another source that identifies individuals.

  • Will not report information that could identify individual establishments (e.g., hospitals).

  • Will not use the data concerning individual establishments for commercial or competitive purposes involving those establishments.

  • Will not use the data to determine rights, benefits, or privileges of individual establishments.

  • Will not identify or attempt to identify any establishment when its identity has been concealed on the database.

  • Will not contact establishments included in the data.

  • Will not attribute to data contributors any conclusions drawn from the data.

  • Will not use data elements from the proprietary severity adjustment software packages (3M APR-DRGs, HSS APS-DRGs, and Medstat Disease Staging) for any commercial purpose or to disassemble, decompile, or otherwise reverse engineer the proprietary software.

  • Must acknowledge the "Healthcare Cost and Utilization Project, (HCUP)", as described in the data use agreement, in reports.

Any violation of the limitations in the data use agreement is punishable under Federal law by a fine of up to $10,000 and up to 5 years in prison. Violations may also be subject to penalties under State statutes.

† The on-line Data Use Agreement training session and the Data Use Agreement are available on the HCUP User Support Website at http://www.hcup-us.ahrq.gov.
‡ Specific provisions are detailed in the Data Use Agreement for Nationwide Inpatient Sample.


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HCUP CONTACT INFORMATION

The NIS Data Use Agreement Training Tool and the Data Use Agreement are available on the AHRQ-sponsored HCUP User Support (HCUP-US) Website:

After completing the on-line training tool, please submit signed data use agreements to HCUP at:

For technical assistance:


WHAT’S NEW IN THE 2005
NATIONWIDE INPATIENT SAMPLE (NIS)?

  • Oklahoma was added to the NIS in 2005. Data from Virginia were not available for inclusion in the 2005 NIS.
  • 2005 NIS Documentation is available exclusively on the HCUP User Support Website (http://www.hcup-us.ahrq.gov) and is no longer included on the NIS CD-ROMs. This ensures that documentation for your data will always be the most recent and up-to-date version.
  • The 10% subsample files are no longer available beginning with the 2005 NIS. The associated data element DISCWT10 was also discontinued.
  • Users must complete an on-line Data Use Agreement training tool prior to receiving the data.

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HEALTHCARE COST AND UTILIZATION PROJECT – HCUP
A FEDERAL-STATE-INDUSTRY PARTNERSHIP IN HEALTH DATA

Sponsored by the Agency for Healthcare Research and Quality

The Agency for Healthcare Research and Quality and
the staff of the Healthcare Cost and Utilization Project (HCUP) thank you for
purchasing the HCUP Nationwide Inpatient Sample ( NIS).



HCUP Nationwide Inpatient Sample ( NIS)

ABSTRACT

The Nationwide Inpatient Sample (NIS) is part of the Healthcare Cost and Utilization Project (HCUP), sponsored by the Agency for Healthcare Research and Quality (AHRQ), formerly the Agency for Health Care Policy and Research.

The NIS is a database of hospital inpatient stays. Researchers and policy makers use the NIS to identify, track, and analyze national trends in health care utilization, access, charges, quality, and outcomes.

The NIS is the largest all-payer inpatient care database that is publicly available in the United States, containing data from 5 to 8 million hospital stays from about 1,000 hospitals sampled to approximate a 20-percent stratified sample of U.S. community hospitals. The NIS is available for an 18-year time period, from 1988 to 2005, allowing analysis of trends over time. (Analyses of time trends are recommended from 1993 forward. See the report, Using the HCUP Nationwide Inpatient Sample to Estimate Trends, available on the HCUP User Support (HCUP-US) Website for details.)

The NIS is the only national hospital database with charge information on all patients, regardless of payer, including persons covered by Medicare, Medicaid, private insurance, and the uninsured. The NIS' large sample size enables analyses of rare conditions, such as congenital anomalies; uncommon treatments, such as organ transplantation; and special patient populations, such as the uninsured.

Inpatient stay records in the NIS include clinical and resource use information typically available from discharge abstracts. Hospital and discharge weights are provided for producing national estimates. The NIS can be linked to hospital-level data from the American Hospital Association's Annual Survey Database and county-level data from the Bureau of Health Professions' Area Resource File, except in those states that do not allow the release of hospital identifiers.

Beginning in 1998, the NIS differs from previous NIS releases: some data elements were dropped; some were added; for some data elements, the coding was changed; and the sampling and weighting strategy was revised to improve the representativeness of the data. (See the report, Changes in the NIS Sampling and Weighting Strategy for 1998, which describes these changes, available on the HCUP-US Website.)

Access to the NIS is open to users who sign data use agreements. Uses are limited to research and aggregate statistical reporting.

For more information on the NIS, please visit the AHRQ-sponsored HCUP-US Website at http://www.hcup-us.ahrq.gov.

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INTRODUCTION TO THE HCUP NATIONWIDE INPATIENT SAMPLE ( NIS )

OVERVIEW OF NIS DATA

The Nationwide Inpatient Sample (NIS) contains all-payer data on hospital inpatient stays from states participating in the Healthcare Cost and Utilization Project (HCUP). Each year of the NIS provides information on approximately 5 million to 8 million inpatient stays from about 1,000 hospitals. All discharges from sampled hospitals are included in the NIS database.

The NIS contains patient-level clinical and resource use information included in a typical discharge abstract. The NIS can be linked directly to hospital-level data from the American Hospital Association (AHA) Annual Survey Database and to county-level data from the Health Resources and Services Administration Bureau of Health Professions’ Area Resource File (ARF), except in those states that do not allow the release of hospital identifiers.

The NIS is designed to approximate a 20-percent sample of U.S. community hospitals, defined by the AHA to be "all non-Federal, short-term, general, and other specialty hospitals, excluding hospital units of institutions." Included among community hospitals are specialty hospitals such as obstetrics-gynecology, ear-nose-throat, short-term rehabilitation, orthopedic, and pediatric institutions. Also included are public hospitals and academic medical centers. Excluded are short-term rehabilitation hospitals (beginning with 1998 data), long-term hospitals, psychiatric hospitals, and alcoholism/chemical dependency treatment facilities.

This universe of U.S. community hospitals is divided into strata using five hospital characteristics: ownership/control, bed size, teaching status, urban/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 stratum. The frame is limited by the availability of inpatient data from the data sources.

In order to improve the representativeness of the NIS, the sampling and weighting strategy was modified beginning with the 1998 data. The full description of this process can be found in the special report on Changes in NIS Sampling and Weighting Strategy for 1998. This report is available on the AHRQ-sponsored HCUP-US Website at http://www.hcup-us.ahrq.gov. To facilitate the production of national estimates, both hospital and discharge weights are provided, along with information necessary to calculate the variance of estimates. Detailed information on the design of the NIS is available in the year-specific special reports on Design of the Nationwide Inpatient Sample found on the HCUP-US Website.

NIS data sets are currently available for multiple years, as shown in Table 1. Each release of the NIS includes:

Table 1. Summary of NIS Releases
 Data from Media/format options Structure of Releases
  • 1988-1992
  • 8 States in 1988
  • 11 States in 1989-1992
On CD-ROM,
in ASCII format
5 years of data in a 6-CD set, compressed files

Two 10% subsamples of discharges for each year
  • 1993
  • 17 states
  • 1994
  • 17 states
  • 1995
  • 19 states
  • 1996
  • 19 states
  • 1997
  • 22 states
  • 1998
  • 22 states
  • 1999
  • 24 states
  • 2000
  • 28 states
  • 2001
  • 33 states
On CD-ROM, in ASCII format 1 year of data in a 2-CD set, compressed files

Two 10% subsamples of discharges for each year
  • 2002
  • 35 states
  • 2003
  • 37 states
  • 2004
  • 37 states
On CD-ROM, in ASCII format 1 year of data in a 2-CD set,compressed files

Two 10% subsamples of discharges for each year

A companion file with four different sets of severity measures
  • 2005
  • 37 states
On CD-ROM, in ASCII format 1 year of data in a 2-CD set, compressed files

A companion file with four different sets of severity measures.

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NIS Data Sources, Hospitals, and Inpatient Stays

Table 2 summarizes the data sources, number of hospitals, and number of unweighted and weighted inpatient stays in NIS data.

Table 2. Summary of NIS Data Sources, Hospitals and Inpatient Stays, 1988-2005
Year Data sources Number of hospitals Number of discharges
in the NIS, unweighted
Number of discharges in the NIS, weighted for national estimates
1988 CA CO FL IL IA MA NJ WA 759 5,265,756 35,171,448
1989 AZ CA CO FL IL IA MA NJ PA WA WI
(Added AZ, PA, WI)
882 6,110,064 35,104,645
1990 AZ CA CO FL IL IA MA NJ PA WA WI
(No change)
871 6,268,515 35,215,397
1991 AZ CA CO FL IL IA MA NJ PA WA WI
(No change)
859 6,156,188 35,036,492
1992 AZ CA CO FL IL IA MA NJ PA WA WI
(No change)
856 6,195,744 35,011,385
1993 AZ CA CO CT FL IL IA KS MD MA
NJ NY OR PA SC WA WI
(Added CT, KS, MD, NY, OR, SC)
913 6,538,976 34,714,530
1994 AZ CA CO CT FL IL IA KS MD MA
NJ NY OR PA SC WA WI
(No change)
904 6,385,011 34,622,203
1995 AZ CA CO CT FL IL IA KS MD MA
MO NJ NY OR PA SC TN WA WI
(Added MO, TN)
938 6,714,935 34,791,998
1996 AZ CA CO CT FL IL IA KS MD MA
MO NJ NY OR PA SC TN WA WI
(No change)
906 6,542,069 34,874,386
1997 AZ CA CO CT FL GA HI IL IA KS MD MA
MO NJ NY OR PA SC TN UT WA WI
(Added GA, HI, UT)
1,012 7,148,420 35,408,207
1998 AZ CA CO CT FL GA HI IL IA KS MD MA
MO NJ NY OR PA SC TN UT WA WI
(No change)
984 6,827,350 34,874,001
1999 AZ CA CO CT FL GA HI IL IA KS MD MA ME MO NJ NY OR PA SC TN UT VA WA WI
(Added ME, VA)
984 7,198,929 35,467,673
2000 AZ CA CO CT FL GA HI IL IA KS KY MD
MA ME MO NC NJ NY OR PA SC TN TX
UT VA WA WI WV
(Added KY, NC, TX, WV)
994 7,450,992 36,417,565
2001 AZ CA CO CT FL GA HI IL IA KS KY MD MA ME MI MN MO NC NE NJ NY OR PA RI SC TN TX UT VA VT WA WI WV
(Added MI, MN, NE, RI, VT)
986 7,452,727
37,187,641
2002 CA CO CT FL GA HI IL IA KS KY MD MA ME MI MN MO NC NE NJ NY NV OH OR PA RI SC SD TN TX UT VA VT WA WI WV
(Added NV, OH, SD; AZ data were not available)
995 7,853,982
37,804,021
2003 AZ CA CO CT FL GA HI IL IN IA KS KY MD MA MI MN MO NC NE NH NJ NY NV OH OR PA RI SC SD TN TX UT VA VT WA WI WV
(Added AZ, IN, NH; ME data were not available)
994 7,977,728 38,220,659
2004 AR AZ CA CO CT FL GA HI IL IN IA KS KY MD MA MI MN MO NC NE NH NJ NY NV OH OR RI SC SD TN TX UT VA VT WA WI WV
(Added AR; PA data were not available)
1,004 8,004,571 38,661,786
2005 AR AZ CA CO CT FL GA HI IL IN IA KS KY MD MA MI MN MO NC NE NH NJ NY NV OH OK OR RI SC SD TN TX UT VT WA WI WV
(Added OK; VA data were not available)
1,054 7,995,048 39,163,834

State-Specific Restrictions

Some data sources that contributed data to the NIS imposed restrictions on the release of certain data elements or on the number and types of hospitals that could be included in the database. Because of confidentiality laws, some data sources were prohibited from providing HCUP with discharge records that indicated specific medical conditions, such as HIV/AIDS or behavioral health. Detailed information on these state-specific restrictions is available in the report, Sources of NIS Data and State-Specific Restrictions, located on the HCUP-US Website (http://www.hcup-us.ahrq.gov).

Contents of CD-ROM Set

The CD-ROM set contains two CD-ROMs that include fixed-width ASCII formatted data files and a README.TXT file describing how to access related NIS documentation on the HCUP-US Website (http://www.hcup-us.ahrq.gov).

CD-ROM #1 contains:

CD-ROM #2 contains:

On the HCUP-US Website (http://www.hcup-us.ahrq.gov), NIS purchasers can access complete file documentation, including variable notes, file layouts, summary statistics, and related technical reports. Similarly, purchasers can also download SAS, SPSS, and Stata load programs. Available online documentation and supporting files are detailed in Table 8.

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NIS Data Elements

All releases of the NIS contain two types of data: inpatient stay records and hospital information with weights. Table 3 and Table 4 (on the following pages) identify the data elements that can be found in the Inpatient Core and Hospital Weights files, respectively. Table 5 identifies the data elements in the Disease Severity Measures files. Table 6 identifies the data elements in the Diagnosis and Procedure Groups files.

Not all data elements in the NIS are uniformly coded or available across all states. The following tables are not complete documentation for the data. Please refer to the NIS documentation located on the HCUP-US Website (http://www.hcup-us.ahrq.gov) for comprehensive information about data elements and the files.

Table 3. Data Elements in the NIS Inpatient Core Files

Data elements that are italicized are not included in the 2005 NIS Inpatient Core Files, but are only available in previous years’ files.

Type of
Data Element
HCUP
Variable Name
Years Available Coding Notes Unavailable in 2005 for:
Admission day of week or weekend AWEEKEND 1998-2005 Admission on weekend: (0) admission on Monday-Friday, (1) admission on Saturday-Sunday  
ADAYWK 1988-1997 Admission day of week: (1) Sunday, (2) Monday, (3) Tuesday, (4) Wednesday, etc.  
Admission month AMONTH 1988-2005 Admission month coded from (1) January to (12) December FL
Admission source ASOURCE 1988-2005 Admission source, uniform coding: (1) ER, (2) another hospital, (3) another facility including long-term care, (4) court/law enforcement, (5) routine/birth/other  
ASOURCE_X 1998-2005 Admission source, as received from data source using State-specific coding  
ASOURCEUB92 2003-2005 Admission source (UB-92 standard coding). For newborn admissions (ATYPE = 4): (1) normal delivery, (2) premature delivery, (3) sick baby, (4) extramural birth; For non-newborn admissions (ATYPE NE 4): (1) physician referral, (2) clinic referral, (3) HMO referral, (4) transfer from a hospital, (5) transfer from a skilled nursing facility, (6) transfer from a another health care facility, (7) emergency room, (8) court/law enforcement, (A) transfer from a critical access hospital  
Admission type ATYPE 1988-2005 Admission type, uniform coding: (1) emergency, (2) urgent, (3) elective, (4) newborn, (5) trauma center beginning in 2003 data, (6) other CA
ELECTIVE 2002-2005 Indicates elective admission: (1) elective, (0) non-elective admission  
Age at admission AGE 1988-2005 Age in years coded 0-124 years  
AGEDAY 1988-2005 Age in days coded 0-365 only when the age in years is less than 1 FL, MA, NH, SC
Clinical Classifications Software (CCS) category DXCCS1 - DXCCS15 1998-2005 CCS category for all diagnoses for NIS beginning in 1998  
DCCHPR1 1988-1997 CCS category for principal diagnosis for NIS prior to 1998. CCS was formerly called the Clinical Classifications for Health Policy Research (CCHPR)  
PRCCS1 - PRCCS15 1998-2005 CCS category for all procedures for NIS beginning in 1998  
PCCHPR1 1988-1997 CCS category for principal procedure for NIS prior to 1998. CCS was formerly called the Clinical Classifications for Health Policy Research (CCHPR)  
Data source information DSNUM 1988-1997 Data source number  
DSTYPE 1988-1997 Data source type: (1) State data organization, (2) Hospital association, (3) Consortia  
Diagnosis information DX1 - DX15 1988-2005 Diagnoses, principal and secondary (ICD-9-CM). Beginning in 2003, the diagnosis array does not include any of external cause of injury codes. These codes have been stored in a separate array ECODEn.  
NDX 1988-2005 Number of diagnoses coded on the original record  
DSNDX 1988-1997 Number of diagnosis fields provided by the data source  
DXSYS 1988-1997 Diagnosis system (ICD-9-CM)  
DXV1 - DXV15 1988-1997 Diagnosis validity flags  
Diagnosis Related Group (DRG) DRG 1988-2005 DRG in use on discharge date  
DRGVER 1988-2005 Grouper version in use on discharge date  
DRG10 1988-1999 DRG Version 10 (effective October 1992 - September 1993)  
DRG18 1998-2005 DRG Version 18 (effective October 2000 - September 2001)  
Discharge quarter DQTR 1988-2005 Coded: (1) Jan - Mar, (2) Apr - Jun, (3) Jul - Sep, (4) Oct - Dec  
Discharge weights
(Weights for 1988-1993 are on Hospital Weights file)
DISCWT 1998-2005 Discharge weight on Core file and Hospital Weights file for NIS beginning in 1998. In all data years except 2000, this weight is used to create national estimates for all analyses. In 2000 only, this weight is used to create national estimates for all analyses excluding those that involve total charges.  
DISCWT_U 1993-1997 Discharge weight on Core file and Hospital Weights file for NIS prior to 1998  
DISCWTcharge 2000 Discharge weight for national estimates of total charges. In 2000 only, this weight is used to create national estimates for analyses that involve total charges  
DISCWT10 1998-2005 Discharge weight on 10% subsample Core file for NIS beginning in 1998. In all data years except 2000, this weight is used to create national estimates for all analyses. In 2000 only, this weight is used to create national estimates for all analyses excluding those that involve total charges  
D10CWT_U 1993-1997 Discharge weight on 10% subsample Core file for NIS prior to 1998  
DISCWTcharge10 2000 Discharge weight for national estimates of total charges on 10% subsample file. In 2000 only, this weight is used to create national estimates for analyses that involve total charges  
Discharge year YEAR 1988-2005    
Disposition of patient (discharge status) DISP 1988-1997 Disposition of patient, uniform coding used prior to 1998: (1) routine, (2) short-term hospital, (3) skilled nursing facility, (4) intermediate care facility, (5) another type of facility, (6) home health care, (7) against medical advice, (20) died  
DIED 1988-2005 Indicates in-hospital death: (0) did not die during hospitalization, (1) died during hospitalization  
DISPUB92 1998-2005 Disposition of patient, UB-92 coding: (1) routine, (2) short term hospital, (3) skilled nursing facility, (4) intermediate care, (5) another type of facility, (6) home health care, (7) against medical advice, (8) home IV provider, (20) died in hospital, (40) died at home, (41) died in a medical facility, (42) died, place unknown, (43) Federal health facility beginning in 2003 data, (50) Hospice, home, (51) Hospice, medical facility, (61) hospital-based Medicare approved swing bed beginning in 2000 data, (62) another rehabilitation facility beginning in 2001 data, (63) long term care hospital beginning in 2001 data, (64) certified nursing facility beginning in 2002 data, (65) psychiatric hospital beginning in 2004 (71) another institution for outpatient services beginning in 2000 data, (72) this institution for outpatient services beginning in 2000 data, (99) discharged alive, destination unknown beginning in 2001 data CA, IN, MD
DISPUNIFORM 1998-2005 Disposition of patient, uniform coding used beginning in 1998: (1) routine, (2) transfer to short term hospital, (5) other transfers, including skilled nursing facility, intermediate care, and another type of facility, (6) home health care, (7) against medical advice, (20) died in hospital, (99) discharged alive, destination unknown  
External causes of injury and poisoning ECODE1 - ECODE4 2003-2005 External cause of injury and poisoning code, primary and secondary (ICD-9-CM). Beginning in 2003, external cause of injury codes are stored in a separate array ECODEn from the diagnosis codes in the array DXn. Prior to 2003, these codes are contained in the diagnosis array (DXn).  
E_CCS1 - E_CCS4 2003-2005 CCS category for the external cause of injury and poisoning codes  
NECODE 2003-2005 Number of external cause of injury codes on the original record. A maximum of 4 codes are retained on the NIS.  
Gender of patient FEMALE 1998-2005 Indicates gender for NIS beginning in 1998: (0) male, (1) female  
SEX 1988-1997 Indicates gender for NIS prior to 1998: (1) male, (2) female  
Hospital information DSHOSPID 1988-2005 Hospital number as received from the data source GA, HI, IN, KS, MI, NE, OH, OK, SC, SD, TN, TX
HOSPID 1988-2005 HCUP hospital number (links to Hospital Weights file)  
HOSPST 1988-2005 State postal code for the hospital (e.g., AZ for Arizona)  
HOSPSTCO 1988-2002 Modified Federal Information Processing Standards (FIPS) State/county code for the hospital links to Area Resource File (available from the Bureau of Health Professions, Health Resources and Services Administration) Beginning in 2003, this data element is available only on the hospital file.  
NIS_STRATUM 1998-2005 Stratum used to sample hospitals, based on geographic region, control, location/teaching status, and bed size. Stratum information is also in the Hospital Weights file.  
Length of Stay LOS 1988-2005 Length of stay, edited  
LOS_X 1988-2005 Length of stay, as received from data source  
Location of the patient PL_UR_CAT4 2003-2005 Urban–rural designation for patient’s county of residence: (1) large metropolitan, (2) small metropolitan, (3) micropolitan, (4) non-core  
Major Diagnosis Category (MDC) MDC 1988-2005 MDC in use on discharge date  
MDC10 1988-1999 MDC Version 10 (effective October 1992 - September 1993)  
MDC18 1998-2005 MDC Version 18 (effective October 2000 - September 2001)  
Median household income for patient's ZIP Code ZIPINC_QRTL 2003-2005 Median household income quartiles for patient's ZIP Code. For 2004, the median income quartiles are defined as: $1 - $35,999; $36,000 - $44,999; $45,000 - $58,999; and $59,000 or more.  
ZIPINC 1998-2002 Median household income category in files beginning in 1998: (1) $1-$24,999, (2) $25,000-$34,999, (3) $35,000-$44,999, (4) $45,000 and above  
ZIPINC4 1988-1997 Median household income category in files prior to 1998: (1) $1-$25,000, (2) $25,001-$30,000, (3) $30,001-$35,000, (4) $35,001 and above  
ZIPINC8 1988-1997 Median household income category in files prior to 1998: (1) $1-$15,000, (2) $15,001-$20,000, (3) $20,001-$25,000, (4) $25,001-$30,000, (5) $30,001-$35,000, (6) $35,001-$40,000, (7) $40,001-$45,000, (8) $45,001 or more  
Neonatal/ maternal flag NEOMAT 1988-2005 Assigned from diagnoses and procedure codes: (0) not maternal or neonatal, (1) maternal diagnosis or procedure, (2) neonatal diagnosis, (3) maternal and neonatal on same record  
Payer information PAY1 1988-2005 Expected primary payer, uniform: (1) Medicare, (2) Medicaid, (3) private including HMO, (4) self-pay, (5) no charge, (6) other  
PAY1_N 1988-1997 Expected primary payer, nonuniform: (1) Medicare, (2) Medicaid, (3) Blue Cross, Blue Cross PPO, (4) commercial, PPO, (5) HMO, PHP, etc., (6) self-pay, (7) no charge, (8) Title V, (9) Worker's Compensation, (10) CHAMPUS, CHAMPVA, (11) other government, (12) other  
PAY1_X 1998-2005 Expected primary payer, as received from the data source  
PAY2 1988-2005 Expected secondary payer, uniform: (1) Medicare, (2) Medicaid, (3) private including HMO, (4) self-pay, (5) no charge, (6) other AZ, CA, CO, FL, HI, IA, NH, OH, OK, RI, SD
PAY2_N 1988-1997 Expected secondary payer, nonuniform: (1) Medicare, (2) Medicaid, (3) Blue Cross, Blue Cross PPO, (4) commercial, PPO, (5) HMO, PHP, etc., (6) self-pay, (7) no charge, (8) Title V, (9) Worker's Compensation, (10) CHAMPUS, CHAMPVA, (11) other government, (12) other  
PAY2_X 1998-2005 Expected secondary payer, as received from the data source AZ, CA, CO, FL, HI, IA, NH, OH, OK, RI, SD
Physician identifiers,
synthetic
MDID_S 1988-2000 Synthetic attending physician number in files prior to 2001  
MDNUM1_R 2003-2005 Re-identified attending physician number in files starting in 2003 CA, CT, GA, HI, IL, IN, MA, NC, OH, OK, UT, VT, WI, WV
MDNUM1_S 2001-2002 Synthetic attending physician number in files beginning in 2001 and discontinued in 2003  
SURGID_S 1988-2000 Synthetic secondary physician number in files prior to 2001  
MDNUM2_R 2003-2005 Re-identified secondary physician number in files starting in 2003 CA, CT, GA, HI, IL, IN, MA, NC, OH, VT, WI, WV
MDNUM2_S 2001-2002 Synthetic secondary physician number in files beginning in 2001 and discontinued in 2003  
Procedure information PR1 - PR15 1988-2005 Procedures, principal and secondary (ICD-9-CM)  
NPR 1988-2005 Number of procedures coded on the original record  
DSNPR 1988-1997 Number of procedure fields in this data source  
PRSYS 1988-1997 Procedure system (ICD-9-CM)  
PRV1 -PRV15 1988-1997 Procedure validity flag  
PRDAY1 1988-2005 Number of days from admission to principal procedure. IL, OH, OK, UT, WA, WV
PRDAY2 - PRDAY15 1998-2005 Number of days from admission to secondary procedures. IL, OH, OK, UT, WA, WV
Race of Patient RACE 1988-2005 Race, uniform coding: (1) white, (2) black, (3) Hispanic, (4) Asian or Pacific Islander, (5) Native American, (6) other GA, IL, KY, MN, NV, OH, OR, WA, WV
Record identifier, synthetic KEY 1998-2005 Unique record number for file beginning in 1998  
SEQ 1988-1997 Unique record number for NIS prior to 1998  
SEQ_SID 1988-1997 Unique record number for NIS prior to 1998  
PROCESS 1988-1997 Processing number for NIS prior to 1998  
Total Charges TOTCHG 1988-2005 Total charges, edited  
TOTCHG_X 1988-2005 Total charges, as received from data source  

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Table 4. Data Elements in the NIS Hospital Weights File

Data elements that are italicized are not included in the 2005 NIS Hospital Weights File, but are only available in previous years’ files.

Type of
Data Element
HCUP
Variable Name
Years Available Coding Notes Unavailable in 2005 for:
Discharge counts N_DISC_U 1988-2005 Number of AHA universe discharges in the stratum  
S_DISC_U 1988-2005 Number of sampled discharges in the sampling stratum (NIS_STRATUM or STRATUM)  
S_DISC_S 1988-1997 Number of sampled discharges in the stratum STRAT_ST  
N_DISC_F 1988-1997 Number of frame discharges in the stratum  
N_DISC_S 1988-1997 Number of State's discharges in the stratum  
TOTAL_DISC 1998-2005 Total number of discharges from this hospital in the NIS  
TOTDSCHG 1988-1997 Total number of discharges from this hospital in the NIS  
Discharge weights DISCWT 1998-2005 Discharge weight used in the NIS beginning in 1998. In all data years except 2000, this weight is used to create national estimates for all analyses. In 2000 only, this weight is used to create national estimates for all analyses excluding those that involve total charges.  
DISCWT_U 1988-1997 Discharge weights used in the NIS prior to 1998.  
DISCWT_F 1988-1997 Discharge weights to the sample frame are available only in 1988-1997  
DISCWT_S 1988-1997 Discharge weights to the State are available only in 1988-1997  
DISCWTcharge 2000 Discharge weight for national estimates of total charges for 2000 only.  
Discharge Year YEAR 1988-2005 Discharge year  
Hospital counts N_HOSP_F 1988-1997 Number of frame hospitals in the stratum  
N_HOSP_S 1988-1997 Number of State's hospitals in the stratum  
N_HOSP_U 1988-2005 Number of AHA universe hospitals in the stratum  
S_HOSP_S 1988-1997 Number of sampled hospitals in STRAT_ST  
S_HOSP_U 1988-2005 Number of sampled hospitals in the stratum (NIS_STRATUM or STRATUM)  
Hospital identifiers HOSPID 1988-2005 HCUP hospital number (links to inpatient Core files)  
AHAID 1988-2005 AHA hospital identifier that matches AHA Annual Survey of Hospitals (not available for all states) GA, HI, IN, KS, MI, NE, OH, OK, SC, SD, TN, TX
IDNUMBER 1988-2005 AHA hospital identifier without the leading 6 (not available for all states) GA, HI, IN, KS, MI, NE, OH, OK, SC, SD, TN, TX
HOSPNAME 1993-2005 Hospital name from AHA Annual Survey of Hospitals (not available for all states) AR, GA, HI, IN, KS, MI, NE, OH, SC, SD, TN, TX
Hospital location HOSPADDR 1993-2004 Hospital address from AHA Annual Survey of Hospitals (not available for all states) AR, GA, HI, IN, KS, MI, NE, OH, OK, SC, SD, TN, TX
HOSPCITY 1993-2005 Hospital city from AHA Annual Survey of Hospitals (not available for all states) AR, GA, HI, IN, KS, MI, NE, OH, OK, SC, SD, TN, TX
HOSPST 1988-2004 Hospital state postal code for hospital (e.g., AZ for Arizona)  
HOSPSTCO 2002-2005 Modified Federal Information Processing Standards (FIPS) State/county code GA, HI, IN, KS, MI, NE, OH, OK, SC, SD, TN, TX
HFIPSSTCO 2005 Unmodified Federal Information Processing Standards (FIPS) State/county code for the hospital. Links to the Area Resource File (available from the Bureau of Health Professions, Health Resources and Services Administration) GA, HI, IN, KS, MI, NE, OH, OK, SC, SD, TN, TX
HOSPZIP 1993-2005 Hospital ZIP Code from AHA Annual Survey of Hospitals (not available for all states) AR, GA, HI, IN, KS, MI, NE, OH, OK, SC, SD, TN, TX
Hospital characteristics HOSP_BEDSIZE 1998-2005 Bed size of hospital: (1) small, (2) medium, (3) large  
H_BEDSZ 1993-1997 Bed size of hospital: (1) small, (2) medium, (3) large  
ST_BEDSZ 1988-1992 Bed size of hospital: (1) small, (2) medium, (3) large  
HOSP_CONTROL 1998-2005 Control/ownership of hospital: (0) government or private, collapsed category, (1) government, nonfederal, public, (2) private, non-profit, voluntary, (3) private, invest-own, (4) private, collapsed category  
H_CONTRL 1993-1997 Control/ownership of hospital: (1) government, nonfederal (2) private, non-profit (3) private, invest-own  
ST_OWNER 1988-1992 Control/ownership of hospital: (1) public (2) private, non-profit (3) private for profit  
HOSP_LOCATION 1998-2005 Location: (0) rural, (1) urban  
H_LOC 1993-1997 Location: (0) rural, (1) urban  
HOSP_LOCTEACH 1998-2005 Location/teaching status of hospital: (1) rural, (2) urban non-teaching, (3) urban teaching  
H_LOCTCH 1993-1997 Location/teaching status of hospital: (1) rural, (2) urban non-teaching, (3) urban teaching  
LOCTEACH 1988-1992 Location/teaching status of hospital: (1) rural, (2) urban non-teaching, (3) urban teaching  
HOSP_REGION 1998-2005 Region of hospital: (1) Northeast, (2) Midwest, (3) South, (4) West  
H_REGION 1993-1997 Region of hospital: (1) Northeast, (2) Midwest, (3) South, (4) West  
ST_REG 1988-1992 Region of hospital: (1) Northeast, (2) Midwest, (3) South, (4) West  
HOSP_TEACH 1998-2005 Teaching status of hospital: (0) non-teaching, (1) teaching  
H_TCH 1993-1997 Teaching status of hospital: (0) non-teaching, (1) teaching  
NIS_STRATUM 1998-2005 Stratum used to sample hospitals beginning in 1998; includes geographic region, control, location/teaching status, and bed size  
STRATUM 1988-1997 Stratum used to sample hospitals prior to 1998; includes geographic region, control, location/teaching status, and bed size  
STRAT_ST 1988-1997 Stratum for State-specific weights  
Hospital weights HOSPWT 1998-2005 Weight to hospitals in AHA universe (i.e., total U.S.) beginning in 1998  
HOSPWT_U 1988-1997 Weight to hospitals in AHA universe (i.e., total U.S.) prior to 1998  
HOSPWT_F 1988-1997 Weight to hospitals in the sample frame.  
HOSPWT_S 1988-1997 Weight to hospitals in the State  

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Table 5. Data Elements in the NIS Disease Severity Measures Files

All data elements listed below are available in the 2005 NIS Disease Severity Measures Files.

Type of
Data Element
HCUP
Variable Name
Years Available Coding Notes
AHRQ Comorbidity Software (AHRQ) CM_AIDS 2002-2005 AHRQ comorbidity measure: Acquired immune deficiency syndrome
CM_ALCOHOL 2002-2005 AHRQ comorbidity measure: Alcohol abuse
CM_ANEMDEF 2002-2005 AHRQ comorbidity measure: Deficiency anemias
CM_ARTH 2002-2005 AHRQ comorbidity measure: Rheumatoid arthritis/collagen vascular diseases
CM_BLDLOSS 2002-2005 AHRQ comorbidity measure: Chronic blood loss anemia
CM_CHF 2002-2005 AHRQ comorbidity measure: Congestive heart failure
CM_CHRNLUNG 2002-2005 AHRQ comorbidity measure: Chronic pulmonary disease
CM_COAG 2002-2005 AHRQ comorbidity measure: Coagulopathy
CM_DEPRESS 2002-2005 AHRQ comorbidity measure: Depression
CM_DM 2002-2005 AHRQ comorbidity measure: Diabetes, uncomplicated
CM_DMCX 2002-2005 AHRQ comorbidity measure: Diabetes with chronic complications
CM_DRUG 2002-2005 AHRQ comorbidity measure: Drug abuse
CM_HTN_C 2002-2005 AHRQ comorbidity measure: Hypertension, uncomplicated and complicated
CM_HYPOTHY 2002-2005 AHRQ comorbidity measure: Hypothyroidism
CM_LIVER 2002-2005 AHRQ comorbidity measure: Liver disease
CM_LYMPH 2002-2005 AHRQ comorbidity measure: Lymphoma
CM_LYTES 2002-2005 AHRQ comorbidity measure: Fluid and electrolyte disorders
CM_METS 2002-2005 AHRQ comorbidity measure: Metastatic cancer
CM_NEURO 2002-2005 AHRQ comorbidity measure: Other neurological disorders
CM_OBESE 2002-2005 AHRQ comorbidity measure: Obesity
CM_PARA 2002-2005 AHRQ comorbidity measure: Paralysis
CM_PERIVASC 2002-2005 AHRQ comorbidity measure: Peripheral vascular disorders
CM_PSYCH 2002-2005 AHRQ comorbidity measure: Psychoses
CM_PULMCIRC 2002-2005 AHRQ comorbidity measure: Pulmonary circulation disorders
CM_RENLFAIL 2002-2005 AHRQ comorbidity measure: Renal failure
CM_TUMOR 2002-2005 AHRQ comorbidity measure: Solid tumor without metastasis
CM_ULCER 2002-2005 AHRQ comorbidity measure: Peptic ulcer disease excluding bleeding
CM_VALVE 2002-2005 AHRQ comorbidity measure: Valvular disease
CM_WGHTLOSS 2002-2005 AHRQ comorbidity measure: Weight loss
All Patient Refined DRG (3M) APRDRG 2002-2005 All Patient Refined DRG
APRDRG_Risk_Mortality 2002-2005 All Patient Refined DRG: Risk of Mortality Subclass
APRDRG_Severity 2002-2005 All Patient Refined DRG: Severity of Illness Subclass
All-Payer Severity-adjusted DRG (HSS, Inc.) APSDRG 2002-2005 All-Payer Severity-adjusted DRG
APSDRG_Mortality_Weight 2002-2005 All-Payer Severity-adjusted DRG: Mortality Weight
APSDRG_LOS_Weight 2002-2005 All-Payer Severity-adjusted DRG: Length of Stay Weight
APSDRG_Charge_Weight 2002-2005 All-Payer Severity-adjusted DRG: Charge Weight
Disease Staging (Medstat) DS_DX_Category1 2002-2005 Disease Staging: Principal Disease Category
DS_Stage1 2002-2005 Disease Staging: Stage of Principal Disease Category
DS_LOS_Level 2002-2005 Disease Staging: Length of Stay Level
DS_LOS_Scale 2002-2005 Disease Staging: Length of Stay Scale
DS_Mrt_Level 2002-2005 Disease Staging: Mortality Level
DS_Mrt_Scale 2002-2005 Disease Staging: Mortality Scale
DS_RD_Level 2002-2005 Disease Staging: Resource Demand Level
DS_RD_Scale 2002-2005 Disease Staging: Resource Demand Scale
Linkage Variables HOSPID 2002-2005 HCUP hospital identification number
KEY 2002-2005 HCUP record identifier

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Table 6. Data Elements in the NIS Diagnosis and Procedure Groups Files

All data elements listed below are available for all states in the 2005 NIS Diagnosis and Procedure Groups files.

Type of
Data Element
HCUP
Variable Name
Years Available Coding Notes
Clinical Classifications Software category for Mental Health and Substance Abuse (CCS-MHSA) CCSMGN1 — CCSMGN15 2005 CCS-MHSA general category for all diagnoses
CCSMSP1 — CCSMSP15 2005 CCS-MHSA specific category for all diagnoses
ECCSMGN1 — ECCSMGN4 2005 CCS-MHSA general category for all external cause of injury codes
Chronic Condition Indicator CHRON1 — CHRON15 2005 Chronic condition indicator for all diagnoses: (0) non-chronic condition, (1) chronic condition
CHRONB1 — CHRONB15 2005 Chronic condition indicator body system for all diagnoses: (1) Infectious and parasitic disease, (2) Neoplasms, (3) Endocrine, nutritional, and metabolic diseases and immunity disorders, (4) Diseases of blood and blood-forming organs, (5) Mental disorders, (6) Diseases of the nervous system and sense organs, (7) Diseases of the circulatory system, (8) Diseases of the respiratory system, (9) Diseases of the digestive system, (10) Diseases of the genitourinary system, (11) Complications of pregnancy, childbirth, and the puerperium, (12) Diseases of the skin and subcutaneous tissue, (13) Diseases of the musculoskeletal system, (14) Congenital anomalies, (15) Certain conditions originating in the perinatal period, (16) Symptoms, signs, and ill-defined conditions, (17) Injury and poisoning, (18) Factors influencing health status and contact with health services
Procedure Class PCLASS1 — PCLASS15 2005 Procedure Class for all procedures: (1) Minor Diagnostic, (2) Minor Therapeutic, (3) Major Diagnostic, (4) Major Therapeutic
Linkage Variables HOSPID 2002-2005 HCUP hospital identification number
KEY 2002-2005 HCUP record identifier

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SAMPLING OF HOSPITALS INCLUDED IN THE NIS

The hospital universe is defined by all hospitals that were open during any part of each calendar year and were designated as community hospitals in the AHA Annual Survey Database.

For more information on how hospitals in the data set were mapped to hospitals as defined by the AHA, refer to the special report, HCUP Hospital Identifiers. For a list of all data sources, refer to Sources of NIS Data and State-Specific Restrictions. For more detailed descriptions of the sampling design, refer to the year-specific special reports, Design of the HCUP Nationwide Inpatient Sample. All reports can be found on the NIS Database Documentation portion of the HCUP-US Website.

Stratification Variables

To help ensure generalizability, five hospital sampling strata were defined based on hospital characteristics contained in the AHA Annual Survey Database. The stratification variables are:

Table 7. Bed Size Categories, by Region
Location and Teaching Status Hospital Bed size
Small Medium Large
NORTHEAST
Rural 1-49 50-99 100+
Urban,non-teaching 1-124 125-199 200+
Urban, teaching 1-249 250-424 425+
MIDWEST
Rural 1-29 30-49 50+
Urban, non-teaching 1-74 75-174 175+
Urban, teaching 1-249 250-374 375+
SOUTH
Rural 1-39 40-74 75+
Urban, non-teaching 1-99 100-199 200+
Urban, teaching 1-249 250-449 450+
WEST
Rural 1-24 25-44 45+
Urban, non-teaching 1-99 100-174 175+
Urban, teaching 1-199 200-324 325+

To further ensure geographic representativeness, implicit stratification variables included state and three-digit ZIP Code (the first three digits of the hospital’s five-digit ZIP Code). The hospitals were sorted according to these variables prior to systematic random sampling. For more detailed descriptions of the stratification and sample design, refer to the year-specific special reports, Design of the HCUP Nationwide Inpatient Sample, which can be found on the HCUP-US Website.

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GETTING STARTED

The NIS data files are provided on CD-ROMs. The NIS Inpatient Core and Hospital Weights files are on CD-ROM #1, while the Disease Severity Measures and Diagnosis and Procedure Groups files are on CD-ROM #2. Comprehensive documentation for the NIS files is available on the HCUP User Support (HCUP-US) Website (http://www.hcup-us.ahrq.gov).

NIS Data Files

In order to load and analyze the NIS data onto your PC, you will need 12 gigabytes of space available. Because of the size of the files, the data are distributed as self-extracting PKZIP compressed files. To decompress the data, you should follow these steps:

  1. Create a directory for the 2005 NIS on your hard drive.
  2. Copy the self-extracting data files from the NIS CD-ROMs into the new directory.
  3. Unzip each file by running the corresponding *.exe file.
    • Type the file name within DOS or click on the name within Windows Explorer.
    • Edit the name of the "Unzip To Folder" in the WinZip Self Extractor dialog to select the desired destination directory for the extracted file.
    • Click on the "Unzip" button.

The ASCII data files will then be uncompressed into this directory. After the files are uncompressed, the *.exe files can be deleted.

NIS Documentation

NIS documentation files on the HCUP-US Website (http://www.hcup-us.ahrq.gov) provide important resources for the user. Refer to these resources to understand the structure and content of the NIS and to aid in using the database.

Table 8 details both the NIS related reports and the comprehensive NIS database documentation available on HCUP-US.

Table 8. NIS Related Reports and Database Documentation Available on HCUP-US
Restrictions on the Use of the NIS
  • Data Use Agreement for the NIS
Corrections to the NIS
  • Information on corrections to the NIS data sets
  • Link to NIS Trends Supplemental Files
Description of the NIS Files
  • Introduction to the NIS, 2005 — this document
  • HCUP Quality Control Procedures — describes procedures used to assess data quality
  • File Specifications — details data file names, number of records, record length, and record layout
  • Sources of NIS Data and State-Specific Restrictions — identifies the NIS data sources and restrictions on sampling and the release of data elements
Load Programs

Programs to load the ASCII data files into statistical software:

  • SAS
  • SPSS
  • Stata
Availability of Data Elements
  • Availability of NIS data elements from 1988-2005
HCUP Tools: Labels and Formats
  • Overview of Clinical Classifications Software (CCS), a categorization scheme that groups ICD-9-CM diagnosis and procedure codes into mutually exclusive categories
  • Label file for CCS categories
  • Label file for multiple versions of Diagnosis Related Groups (DRGs)
  • NIS SAS format library program to create a value labels
  • NIS ICD-9-CM formats to label ICD-9-CM diagnoses and procedures
  • IS Severity formats to label severity data elements
Description of Data Elements in the NIS
  • Description of Data Elements — details uniform coding and state-specific idiosyncrasies
  • Summary Statistics — lists means and frequencies on nearly all data elements
  • NIS Severity Measures — provides detailed documentation on the different types of measures
  • HCUP Coding Practices — describes how HCUP data elements are coded
  • HCUP Hospital Identifiers — explains data elements that characterize individual hospitals
NIS Related Reports

Links to HCUP-US page with various NIS-related reports such as the following:

  • Design of the Nationwide Inpatient Sample for 1988 to 2005
  • Changes in NIS Sampling and Weighting Strategy for 1998
  • Calculating Nationwide Inpatient Sample Variances
  • Using the HCUP Nationwide Inpatient Sample to Estimate Trends
  • NIS Comparison Reports (available for years in which the NIS sample changed)
  • HCUP Data Quality Reports for 1988-2005
HCUP Supplemental Files
  • Cost-to-Charge Ratio files
  • Hospital Market Structure files
  • NIS Trends Supplemental files

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HOW TO USE THE NIS

This section provides a brief synopsis of special considerations when using the NIS. For more details, refer to the comprehensive documentation on the HCUP-US Website (http://www.hcup-us.ahrq.gov).

Calculating National Estimates

NIS Year Name of Discharge Weight on the Core File to Use for Creating Nationwide Estimates Name of Discharge Weight on the 10% Subsample Core File to Use for Creating Nationwide Estimates
2005
  • DISCWT for all analyses
  • The 10% Subsample Core File was discontinued with the 2005 NIS.
2001 - 2004
  • DISCWT for all analyses
  • DISCWT10 for all analyses
2000
  • DISCWT to create nationwide estimates for all analyses except those that involve total charges.
  • DISCWTCHARGE to create nationwide estimates of total charges. 
  • DISCWT10 to create nationwide estimates for all analyses except those that involve total charges.
  • DISCWTCHARGE10 to create nationwide estimates of total charges. 
1998 - 1999
  • DISCWT for all analyses
  • DISCWT10 for all analyses
1988 - 1997
  • DISCWT_U for all analyses
  • D10CWT_U for all analyses

Studying Trends

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Choosing Data Elements for Analysis

ICD-9-CM Diagnosis and Procedure Codes

The collection and reporting of external cause of injury (E codes) varies greatly across states. Some states have laws or mandates for the collection of E codes; others do not. Some states do not require hospitals to report E codes in the range E870-E879 - "misadventures to patients during surgical and medical care" - which means that these occurrences will be underreported. Be sure to read the state-specific notes on diagnoses for more details; this information can be found on the Description of Data Elements page on the HCUP-US Website (http://www.hcup-us.ahrq.gov/db/nation/nis/nisdde.jsp).

OTHER HCUP PRODUCTS

Information on HCUP products and services is available on the AHRQ-sponsored HCUP User Support Website at http://www.hcup-us.ahrq.gov

DATABASES

For more information on all HCUP databases, visit the HCUP-US Website at http://www.hcup-us.ahrq.gov or contact the HCUP Central Distributor (detailed below).

Nationwide Inpatient Sample (NIS) is a nationwide database of hospital inpatient stays. The NIS is the largest all-payer inpatient care database that is publicly available in the United States, containing data from 5 to 8 million hospital stays from about 1,000 hospitals sampled to approximate a 20-percent stratified sample of U.S. community hospitals. The NIS has been available since 1988. For trends analysis, it is recommended that analyses begin with the 1993 data year.

State Inpatient Databases (SID) are hospital inpatient databases from Data Organizations participating in HCUP. The SID contain the universe of the inpatient discharge abstracts in the participating HCUP states, translated into a uniform format to facilitate multi-State comparisons and analyses.

State Ambulatory Surgery Databases (SASD) are outpatient databases from Data Organizations in participating HCUP States; these databases capture surgeries performed on the same day in which patients are admitted and released. The SASD contain the ambulatory surgery encounter abstracts in participating States, translated into a uniform format to facilitate multi-state comparisons and analyses. All of the databases include abstracts from hospital-affiliated ambulatory surgery sites. Some contain the universe of ambulatory surgery encounter abstracts for that state, including records from both hospital-affiliated and freestanding surgery centers. Composition and completeness of data files may vary from state to state.

The State Emergency Department Databases (SEDD) include data on all emergency department visits that do not result in an admission from Data Organizations in participating HCUP states that provide ED data. Information on patients initially seen in the emergency room and then admitted to the hospital is included in the SID. All of the databases include abstracts from hospital-affiliated emergency department sites. Composition and completeness of data files may vary from state to state.

Kids' Inpatient Database (KID) is a unique database of hospital inpatient stays for children. The KID has been produced every three years since 1997 and was specifically designed to permit researchers to study a broad range of conditions and procedures related to child health issues.

HCUP CENTRAL DISTRIBUTOR

HCUP databases are available for purchase through the AHRQ-sponsored HCUP Central Distributor. All years of the NIS and KID are released through the HCUP Central Distributor. In addition, many of the HCUP State Partners allow the public release of the HCUP SID, SASD, and SEDD through the HCUP Central Distributor. Application Kits for purchasing the HCUP databases are available online at http://www.hcup-us.ahrq.gov or by contacting the HCUP Central Distributor directly. Information on how to obtain uniformly-formatted HCUP files from states not participating in the HCUP Central Distributor is also available from the HCUP Central Distributor:

HCUP Central Distributor
Phone: (866) 556-4287 (toll-free)
FAX: (866) 792-5313
E-mail: HCUPDistributor@ahrq.gov

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HCUP USER SUPPORT

HCUP User Support (HCUP-US) provides technical assistance to all HCUP users and is designed to facilitate the use of HCUP data, software tools, and products. The goals of this service are to increase awareness of the strengths and uses of HCUP data and to enhance the skills of individuals using the data for research, education, and policy analysis. A user-friendly Website for HCUP-US is located at http://www.hcup-us.ahrq.gov. This site includes links to information on how to purchase and understand the HCUP databases, as well as links to HCUP User Support Services and an index of HCUP topics. For further information, consultants are available via both telephone and e-mail to help in planning analytic research and to offer advice about appropriate uses of HCUP data.

HCUPnet

HCUPnet is a Web-based query tool for identifying, tracking, analyzing, and comparing statistics on hospitals at the national, regional, and state level. HCUPnet offers easy access to national statistics and trends and selected state statistics about hospital stays. This tool provides step by step guidance, helping researchers to quickly obtain the statistics they need. HCUPnet generates statistics using the NIS, KID, and SID for those states that have agreed to participate. In addition, HCUPnet provides Quick Statistics — ready-to-use tables on commonly requested information — as well as national statistics based on the AHRQ Quality Indicators. HCUPnet can be found at: http://hcupnet.ahrq.gov/.

TOOLS

AHRQ Quality Indicators (QIs) are clinical performance measures for use with readily available inpatient data. Methods and software for the AHRQ Quality Indicators can be downloaded from http://www.qualityindicators.ahrq.gov.

The following tools can all be found at the HCUP User Support Website, Tools and Software page, at http://www.hcup-us.ahrq.gov/tools_software.jsp. Methods and software related to these products can be downloaded from the same Web page.

PUBLICATIONS

Publications using HCUP data or describing methods for using HCUP data can be found at: http://www.hcup-us.ahrq.gov/reports.jsp.

HCUP Fact Books report aggregate statistics and detailed analyses using HCUP data. The Fact Books can be viewed online or can be requested from the AHRQ Publications Clearinghouse at (800) 358 9295. You can also send a postcard requesting these reports by writing to: AHRQ Publications Clearinghouse, P.O. Box 8547, Silver Spring, MD 20907.

HCUP Statistical Briefs are Web-based reports that present simple, descriptive statistics on a variety of focused topics such as hospital admissions through the emergency department, hospitalizations among the uninsured, women and heart disease, hospital stays associated with alcohol abuse, and racial and ethnic disparities in potentially preventable hospitalizations.

HCUP Methods Series features a broad array of methodological reports on the HCUP databases and software tools. Topics range from how to use the NIS for reporting trends, how to properly calculate variance estimates using the NIS, an evaluation of linking patients across hospital stays in the SID, evaluations of HCUP emergency department and ambulatory surgery data, an evaluation of E code reporting across the HCUP States, and creation of utilization flags based on UB-92 revenue codes.

HCUP Database Reports are specific to the design and use of the HCUP databases. These reports include descriptions of the design of each database, comparisons of HCUP data with other data sources, evaluations of data quality, and descriptions of database composition.

New Findings and Publications based on HCUP data are available at the AHRQ Website at http://www.ahrq.gov/data/hcup/hcupref.htm. Publications are listed by author and information includes title, publication, data, and often access to an abstract.

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Internet Citation: 2005 Introduction to the NIS. Healthcare Cost and Utilization Project (HCUP). February 2011. Agency for Healthcare Research and Quality, Rockville, MD. www.hcup-us.ahrq.gov/db/nation/nis/NIS_Introduction_2005.jsp.
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