Issued June 2004

Updated November 2015

Agency for Healthcare Research and Quality
Healthcare Cost and Utilization Project (HCUP)

Phone: (866) 290-HCUP (4287)
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: (301) 628-3201
E-mail: hcup@s-3.com

Table of Contents

• SUMMARY OF DATA USE LIMITATIONS


• HCUP CONTACT INFORMATION


• WHAT’S NEW IN THE 2002 NATIONWIDE INPATIENT SAMPLE (NIS)?


• ABSTRACT


• INTRODUCTION TO THE HCUP NATIONWIDE INPATIENT SAMPLE (NIS)


• OVERVIEW OF NIS DATA
• NIS Data Sources, Hospitals, and Inpatient Stays
• State-Specific Restrictions
• Contents of CD-ROM Set
• NIS Data Elements


• SAMPLING OF HOSPITALS INCLUDED IN THE NIS
• Stratification Variables


• GETTING STARTED
• NIS Data Files
• NIS Documentation


• HOW TO USE THE NIS
• Creating National Estimates
• Why the NIS Should not be Used to Make State-Level Estimates
• Studying Trends
• Choosing Data Elements for Analysis
• ICD-9-CM Diagnosis and Procedure Codes


• OTHER HCUP PRODUCTS
• DATABASES
• HCUP CENTRAL DISTRIBUTOR
• HCUP USER SUPPORT
• HCUPnet
• TOOLS
• PUBLICATIONS

Index of Tables

• Table 1. Summary of NIS Releases
• Table 2. Summary of NIS Data Sources, Hospitals and Inpatient Stays, 1988-2002
• Table 3. Data Elements in the NIS Inpatient Core Files
• Table 4. Data Elements in the NIS Hospital Weights File
• Table 5. Data Elements in the NIS Disease Severity Measures Files
• Table 6. Bed Size Categories, by Region
• Table 7. NIS Documentation CD-ROM, including Severity Adjustment Files

HCUP CONTACT INFORMATION

All HCUP data users, including data purchasers and collaborators, must complete the online HCUP Data Use Agreement (DUA) Training Tool, and read and sign the HCUP Data Use Agreement. Proof of training completion and signed Data Use Agreements must be submitted to the HCUP Central Distributor as described below.

The on-line DUA training course is available at: http://www.hcup-us.ahrq.gov/tech_assist/dua.jsp.

The HCUP Nationwide Data Use Agreement are is available on the AHRQ-sponsored HCUP User Support (HCUP-US) website at:

http://www.hcup-us.ahrq.gov

HCUP Central Distributor

Data purchasers will be required to provide their DUA training completion code and will execute their DUAs electronically as a part of the online ordering process. The DUAs and training certificates for collaborators and others with access to HCUP data should be submitted directly to the HCUP Central Distributor using the contact information below.

The HCUP Central Distributor can also help with questions concerning HCUP database purchases, your current order, training certificate codes, or invoices, if your questions are not covered in the Purchasing FAQs on the HCUP Central Distributor website.

Purchasing FAQs:
https://www.distributor.hcup-us.ahrq.gov/Purchasing-Frequently-Asked-Questions.aspx

Phone: 866-556-HCUP (4287) (toll free)
Email: HCUPDistributor@AHRQ.gov
Fax: 866-792-5313 (toll free in the United States)

Mailing address:
HCUP Central Distributor
Social & Scientific Systems, Inc.
8757 Georgia Ave, 12th Floor
Silver Spring, MD 20910

HCUP User Support:

Information about the content of the HCUP databases is available on the HCUP User Support (HCUP-US) website (http://www.hcup-us.ahrq.gov). If you have questions about using the HCUP databases, software tools, supplemental files, and other HCUP products, please review the HCUP Frequently Asked Questions or contact HCUP User Support:

HCUP FAQs:
http://www.hcup-us.ahrq.gov/tech_assist/faq.jsp

Phone: 866-290-HCUP (4287) (toll free)
Email: hcup@ahrq.gov

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 users for
purchasing the HCUP National Inpatient Sample (NIS).

HCUP National 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 policymakers use the NIS to identify, track, and analyze national trends in healthcare 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 1000 hospitals sampled to approximate a 20-percent stratified sample of U.S. community hospitals. The NIS is available for a 15-year time period, from 1988 to 2002, allowing analysis of trends over time.

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's 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 of Hospitals 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.

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, visit the AHRQ-sponsored HCUP User Support (HCUP-US) Website at http://www.hcup-us.ahrq.gov or see the detailed documentation on the documentation CD that accompanies the data.

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 of Hospitals 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 nonfederal, 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 2002 NIS Documentation CD-ROM and on the AHRQ-sponsored HCUP User Support 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 NIS Documentation CD-ROM.

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

• Data in fixed-width ASCII format on CD-ROM.
• Patient-level hospital discharge abstract data for 100 percent of discharges from a sample of hospitals in participating States.
• 5 million to 8 million inpatient records per year.
• 800-1,000 hospitals per year.
• Two 10% subsamples of discharges from all NIS hospitals.
• Discharge-level weights to calculate national estimates for discharges.
• Hospital Weights File to produce national estimates for hospitals and to link the NIS to data from the American Hospital Association Annual Survey of Hospitals.
• NIS Documentation and tools, also on CD-ROM — including file specifications, programming source code for loading ASCII data into SAS and SPSS, and value labels.

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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.

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 on Sources of NIS Data and State-specific Restrictions on the NIS Documentation CD-ROM.

Contents of CD-ROM Set

There are two types of files included in the NIS: 1) data files and 2) documentation and tools files.

1. Data Files - four types of fixed-width ASCII formatted data files are included in the NIS, beginning with the 2002 data:
   
   Inpatient Core File: This inpatient discharge-level file contains data for 100% of the discharges from a sample of hospitals in participating states. The unit of observation is an inpatient stay record. See Table 3 for a list of data elements in the Inpatient Core File. This file is available in all years.
   
   Subsample Inpatient Core Files: Each of these discharge-level files contain all data elements from the Core File for a 10% subsample of discharges from the NIS; these can be combined to create a 20% NIS subsample. These files can be useful for testing programs or validating models. The unit of observation is an inpatient stay record. See Table 3 for a list of data elements in the Inpatient Core Files. These files are available in all years.
   
   Hospital Weights File: This hospital-level file contains one observation for each hospital included in the NIS and contains weights and variance estimation data elements, as well as linkage data elements. The unit of observation is the hospital. The HCUP hospital identifier (HOSPID) provides the linkage between the NIS Inpatient Core files and the Hospital Weights file. See Table 4 for a list of data elements in the Hospital Weights File. This file is available in all years.
   
   Disease Severity Measures Files: These discharge-level files contain information from four different sets of disease severity measures. Information from these severity files is to be used in conjunction with the inpatient Core files. There is one severity measure file for each of the Core and subsample Core files. The unit of observation is an inpatient stay record. The HCUP unique record identifier (KEY) provides the linkage between the Core files and the Disease Severity Measures files. See Table 5 for a list of data elements in the Severity Measures Files. These files are available beginning with the 2002 NIS.


2. Documentation and Tools Files
   
   Documentation: Complete file documentation, variable notes, and summary statistics are provided in a series of Portable Document Format (*.pdf) files. These files are detailed in Table 7.
   
   SAS source code: Code is included for the format library for the variables and for loading ASCII data into SAS format.
   
   SPSS source code: Code is included for the variable library and for loading ASCII data into SPSS format.
   
   Labels: Labels for the Clinical Classifications Software (CCS), formerly called the Clinical Classifications for Health Policy Research (CCHPR), and for the Diagnosis-Related Groups (multiple versions).
   
   File Specifications: Record layouts for all data files.

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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 stay and hospital weights files, respectively. Beginning with the 2002 NIS, an additional file including four different sets of disease severity measures is available. Table 5 identifies the data elements in the disease severity measures files.

Not all data elements in the NIS are uniformly coded or available across all States. This is not complete documentation for the data; please refer to the NIS Documentation CD-ROM for full documentation on all data elements, for summary statistics, and for the record layout.

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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 of Hospitals.

For more information on how hospitals in the data 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 Documentation CD-ROM.

Stratification Variables

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

• Geographic Region – Northeast, Midwest, West, or South. This is based on the U.S. Census regions.
• Location – urban or rural. A metropolitan statistical area is considered urban.
• Teaching Status – teaching or non-teaching. A hospital is considered to be a teaching hospital if it has an AMA-approved residency program, is a member of the Council of Teaching Hospitals (COTH) or has a ratio of full-time equivalent interns and residents to beds of .25 or higher.
• Control – government nonfederal (public), private not-for-profit (voluntary) or private investor-owned (proprietary). When there were enough hospitals of each type to allow it (southern rural, southern urban non-teaching, and western urban non-teaching), hospitals were stratified as public, voluntary, and proprietary. For smaller strata (north central rural and western rural hospitals) a collapsed stratification of public versus private was used, with the voluntary and proprietary hospitals combined to form a single ‘private’ category. For all other combinations of region, location and teaching status, no stratification based on control was advisable given the number of hospitals in these cells.
• Bed size – small, medium, or large. Bed size categories are based on hospital beds, and are specific to the hospital's location and teaching status, as shown in Table 6 (on the following page). Bed size cutpoints were chosen so that approximately one-third of the hospitals in a given region and location/teaching combination would be in each bed size category (small, medium, or large). Rural hospitals were not split according to teaching status, because rural teaching hospitals were rare.

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 NIS Documentation CD-ROM.

GETTING STARTED

NIS information is provided on two CD-ROMs. The NIS inpatient core and hospital weights data files are on CD-ROM #1, and the NIS documentation and tools and the disease severity measures files are on CD-ROM #2.

NIS Data Files

In order to load and analyze the NIS data onto your PC, you will need 10 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 NIS on your hard drive.
2. Copy the self-extracting data files from the NIS Data Files CD-ROM 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 Documentation CD-ROM 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 NIS. Many of the documentation files are provided in portable document format (*.pdf) files. Files with the *.pdf extension can be viewed, searched, and printed using the Adobe Acrobat Reader®.

You must have the Adobe Acrobat Reader software on your computer to access the NIS documentation. If you do not have Adobe Acrobat Reader software on your computer, see the DOCUMENTATION.README.TXT file on NIS Documentation CD-ROM for instructions on installing or obtaining the software.

The Acrobat Reader provided on the NIS Documentation CD-ROM is for IBM-compatible microcomputers running Microsoft Windows 98, second edition, or higher. More information and Acrobat Reader software for other platforms (DOS, Windows 3.1, Macintosh, Sun Systems, etc.) may be obtained free of charge from the Adobe Home Page at http://www.adobe.com/. For further assistance in installing and running the Adobe Acrobat Reader on your computer platform, please consult your local support personnel.

Table 7 describes the documentation, tools, and the severity adjustment data files that can be found on the NIS Documentation CD-ROM and illustrates the structure of the directories and subdirectories on the CD. All NIS documentation is also available on the AHRQ-sponsored HCUP User Support Website at http://www.hcup-us.ahrq.gov.

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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 see detailed documentation under Special Reports, Description of Data Elements, and Summary Statistics.

• If anyone other than the original purchaser uses the NIS data, be sure to have them read and sign a data use agreement. A copy of the signed data use agreements must be sent to AHRQ. See page 2 for the mailing address. A copy of the NIS Data Use Agreement is provided in the binder you receive when you purchase the NIS and is available on the HCUP User Support Website: http://www.hcup-us.ahrq.gov.
• The NIS contains discharge-level records, not patient-level records. This means that individual patients who are hospitalized multiple times in one year may be present in the NIS multiple times. There is no uniform patient identifier available that allows a patient-level analysis with the NIS. This will be especially important to remember for certain conditions for which patients may be hospitalized multiple times in a single year.

Creating National Estimates

• To produce national estimates, use one of the following discharge weights to weight discharges in the NIS Core files to the discharges from all U.S. community, non-rehabilitation hospitals. The name of the discharge weight data element depends on the year of data, the type of analysis, and whether you are using the Core file or the 10% subsample Core file.

• Because the NIS is a stratified sample, proper statistical techniques must be used to calculate standard errors and confidence intervals. For detailed instructions, refer the special report Calculating Nationwide Inpatient Sample Variances on the NIS Documentation CD-ROM.
• The NIS Comparison Report provides an assessment of the accuracy of NIS estimates. The most recent NIS Comparison Report is provided on the NIS Documentation CD-ROM. The updated NIS Comparison Report for the current NIS will be available on the HCUP User Support Website later in the year of data release (e.g., the 2002 Comparison Report will be available in fall of 2004).
• When creating national estimates, it is a good idea to check your estimates against other data sources, if available.  For example, the National Hospital Discharge Survey (http://www.cdc.gov/nchs/products/pubs/pubd/series/sr13/ser13.htm) can provide benchmarks against which to check your national estimates for hospitalizations with more than 5000 cases. 
• When using the 10% subsample files, use the specially created subsample weight, DISCWT10 (the discharge weight multiplied by 10). When using the hospital weights with the subsample files, there is no need to multiply the hospital weights because all hospitals will be represented in the subsample files.

Why the NIS Should not be Used to Make State-Level Estimates

AHRQ strongly advises researchers against using the NIS to estimate State-specific statistics. Prior to 2012, State is available as a NIS data element. However, these NIS samples were not designed to yield a representative sample of hospitals at the State level. AHRQ recommends that researchers employ the SID for State-level estimates.

Each NIS sample is drawn from the sampling frame consisting of discharge data submitted by HCUP Partners-statewide data organizations that agree to participate in the NIS. Data from non-Partner States are missing completely from the sampling frame, and data from Partner States are sometimes incomplete because of different State reporting requirements, different State restrictions, or other data omissions. The NIS is designed to represent hospitals and discharges nationally, including those outside the sampling frame.

To accomplish this, within each hospital sampling stratum the NIS draws a number of hospitals from the sampling frame required to net a total of 20 percent of hospitals nationally. The sampling strata are defined by census region (4 regions), hospital ownership (3 categories), urban-rural location, teaching status, and bed size (3 categories). As a result, the proportion of NIS hospitals in a stratum that are from a given State is unlikely to equal the State's actual proportion of hospitals in that stratum. Consequently, the sample of NIS hospitals is unlikely to be representative of hospitals in the State, and the NIS sample weights will not be appropriate at the State level.

The level of this "misrepresentation" varies across the States in any given year of the NIS, which further confounds State-to-State comparisons on the basis of State-specific estimates from the NIS. Moreover, for a given State the level of misrepresentation changes from year to year as States (and hospitals) enter and exit the sampling frame over time. This further confounds State-specific trends on the basis of State-specific estimates from the NIS.

Finally, because the NIS was not designed to be representative at the State level, design-based estimates of standard errors are not possible, which severely hampers State-level inferences. Moreover, the NIS is composed of all discharges from a sample of hospitals (a cluster sample). The hospital-to-hospital variation and the small number of hospitals available in the NIS for many States make Statelevel estimates very imprecise at best and biased at worst.

Studying Trends

• When studying trends over time using the NIS, be aware that the sampling frame for the NIS changes almost annually, i.e., more states have been added over time. Estimates from earlier years of the NIS may be subject to more sampling bias than later years of the NIS.
• Short-term rehabilitation hospitals are included in the 1988-1997 NIS, but are excluded from the NIS beginning in 1998. Patients treated in short-term rehabilitation hospitals tend to have lower mortality rates and longer lengths of stay than patients in other community hospitals. The elimination of rehabilitation hospitals may affect trends but the effect is likely small since only about 3 percent of community hospitals are short-term rehabilitation hospitals and not all state data sources included short term rehabilitation hospitals.

Choosing Data Elements for Analysis

• For all data elements you plan to use in your analysis, first perform descriptive statistics and examine the range of values, including number of missing cases. Summary statistics for the entire NIS are provided in the "Summary Statistics" directory on the NIS Documentation CD-ROM. When you detect anomalies (such as large numbers of missing cases), perform descriptive statistics by state for that variable to detect if there are state-specific differences. Sometimes performing descriptive statistics by hospital can be helpful to detect hospital-specific data anomalies.
• Not all data elements in the NIS are provided by each state data source. These data elements are provided on the NIS because they can be valuable for research purposes but they should be used cautiously. For example, RACE is missing for a number of states thus national estimates using RACE should be interpreted and reported with caveats. Check the documentation and run frequencies by state to identify if a data element is not available in one or more states.
• There are differences across the state data sources in the collection of information that could not be accounted for during HCUP processing to make the data uniform. Be sure to read state-specific notes for each data element that you use in your analysis — this information can be found under "Description of Data Elements" on the NIS Documentation CD-ROM.
• Data elements with "_X" suffixes contain state-specific coding, i.e., these data elements are provided by the data sources and have not been altered in any way. For some data elements (e.g., LOS_X and TOTCHG_X) this means that no edit checks have been applied. For other data elements (e.g., PAY1_X), the coding is specific to each state and may not be comparable to any other state.

ICD-9-CM Diagnosis and Procedure Codes

• ICD-9-CM diagnosis and procedure codes provide valuable insights into the reasons for hospitalization and what procedures patients receive, but these codes need to be carefully used and interpreted. ICD-9-CM codes change every October as new codes are introduced and some codes are retired.
• Although the NIS contains up to 15 diagnoses and 15 procedures, the number of diagnoses and procedures varies by state. Some states provide as many as 30 diagnoses and 21 procedures, while other states provide as few as 10 diagnoses and 6 procedures. Because very few cases have more than 15 diagnoses or procedures, the diagnosis and procedure vectors were truncated to save space in the NIS data files. Two variables are provided which tell you exactly how many diagnoses and procedures were on the original records (NDX and NPR).
• 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 870-879 "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 can be found under "Description of Data Elements" on the NIS Documentation CD-ROM.

OTHER HCUP PRODUCTS

Information on HCUP products and services is available on the World Wide Web on the AHRQ Website https://www.ahrq.gov/research/data/hcup/index.html. HCUP User Support is available at http://www.hcup-us.ahrq.gov.

DATABASES

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 1000 hospitals sampled to approximate a 20-percent stratified sample of U.S. community hospitals. The NIS is available for a 15-year time period, from 1988 to 2002, allowing analysis of trends over time. For more information, visit the HCUP User Support Website at http://www.hcup-us.ahrq.gov or contact the HCUP Central Distributor (detailed below).

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. Together, the SID encompass about 85 percent of all U.S. community hospital discharges in 2002. For more information, visit the HCUP User Support Website at http://www.hcup-us.ahrq.gov or contact the HCUP Central Distributor (see below).

State Ambulatory Surgery Databases (SASD)are outpatient databases from Data Organizations in participating HCUP States, which 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. For more information, visit the HCUP User Support Website at http://www.hcup-us.ahrq.gov or contact the HCUP Central Distributor (see below).

Kids' Inpatient Database (KID)) is a unique database of hospital inpatient stays for children 18 years of age and younger. The 1997 and 2000 KID was specifically designed to permit researchers to study a broad range of conditions and procedures related to child health issues. The KID is created and released every three years. For more information, visit the HCUP User Support Website at http://www.hcup-us.ahrq.gov or contact the HCUP Central Distributor (see below).

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 State Inpatient Databases (SID) and State Ambulatory Surgery Databases (SASD) through the HCUP Central Distributor. Application Kits for purchasing the HCUP databases are available online at http://www.hcup-us.ahrq.gov or contact 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: (301) 628-3201
E-mail: hcup@s-3.com

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 Frequently Asked Questions. 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. With HCUPnet you have easy access to national statistics and trends and selected state statistics about hospital stays. HCUPnet guides you step by step to obtain the statistics you need. HCUPnet generates statistics using the Nationwide Inpatient Sample (NIS), the Kids' Inpatient Database (KID), and the State Inpatient Databases (SID) for those states that have agreed to participate. In addition, HCUPnet provides Quick Statistics — ready-to-use tables on commonly requested information — and national statistics based on the AHRQ Quality Indicators. HCUPnet can be found at: http://www.ahrq.gov/legacy/qual/kt/hcupnet/hcupsumm.htm.

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/.

Clinical Classifications Software (CCS), formerly known as the Clinical Classifications for Health Policy Research (CCHPRs), are classification systems that group ICD-9-CM diagnoses and procedures into a limited number of clinically meaningful categories. Methods and software can be downloaded from the HCUP User Support Website, Tools and Software page, at http://www.hcup-us.ahrq.gov/tools_software.jsp.

Comorbidity Software assigns variables that identify comorbidities in hospital discharge records using ICD 9 CM diagnosis codes (International Classification of Diseases, Ninth Revision, Clinical Modification). Methods and software can be downloaded from the HCUP User Support Website, Tools and Software page, at http://www.hcup-us.ahrq.gov/tools_software.jsp.

Procedure Classes identify whether a procedure is (a) diagnostic or therapeutic, and (b) minor or major in terms of invasiveness and/or resource use. Software can be found at http://www.hcup-us.ahrq.gov/tools_software.jsp.

PUBLICATIONS

HCUP Research Notes and Fact Books report aggregate statistics and detailed analyses using HCUP data. To request copies, contact the AHRQ Publications Clearinghouse at (800) 358 9295 or send a postcard to: AHRQ Publications Clearinghouse, P.O. Box 8547, Silver Spring, MD 20907 or visit http://www.hcup-us.ahrq.gov/reports.jsp.

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