The NIS Trends Supplemental files (NIS-Trends) are discharge-level files that provide the NIS data user with both the trend weights and data elements that are consistently defined across data years. They are part of a family of databases and software tools developed as part of the Healthcare Cost and Utilization Project (HCUP), a Federal-State-Industry partnership sponsored by the Agency for Healthcare Research and Quality. HCUP databases, tools, and software inform decision making at the national, State, and community levels.

Contents:

• Overview
• How Are the NIS-Trends Files Used?
• What NIS-Trends Files Are Available?
• Hardware and Software Requirements
• User Guide
• How Can Users Obtain the NIS-Trends Files?
• File Specifications?

The NIS contains all-payer data on hospital inpatient stays from states participating in HCUP. The NIS includes all discharges from an approximate 20 percent stratified sample of U.S. community hospitals. Several revisions have been made to the NIS sample design since its inception. First, the sampling frame changed over time as more states made their data available to HCUP. The 1988 NIS was drawn from a frame of eight states representing 31 percent of the U.S. population. In contrast, later years of the NIS were drawn from a frame of states representing 85 to 90 percent of the U.S. population. Second, in 1998 the sampling method changed to better reflect the cross-sectional population of hospitals. The hospital stratification variables were redefined, short-term rehabilitation facilities were dropped from the target universe, and sampling preference was no longer given to prior-year NIS hospitals. Third, the definitions and availability of data elements in the NIS changed over time. Analysts who want to use the NIS to estimate trends in patient and hospital outcomes need to adjust for these changes.

The purpose of the NIS Trends Supplemental files (NIS-Trends) is to ease the burden on researchers conducting analyses that span multiple years. A previous study, Using the HCUP Nationwide Inpatient Sample to Estimate Trends, evaluated the changes in the NIS design and provided data users with an alternate set of NIS discharge and hospital weights for the 1988-1997 HCUP NIS. The NIS-Trends files build on this earlier work and provide the data user with both the trend weights and data elements that are consistently defined across data years. Based primarily on the addition of states to HCUP over time, it is recommended that trend analyses should exclude the 1988 – 1992 period and begin with 1993. The following table enumerates the differences in weighted discharges:

The NIS-Trends files were designed to be merged with the NIS Core files to produce a dataset containing the complete set of variables from both sources. The NIS-Trends CD-ROMs contain the NIS-Trends data files, documentation, load programs for SAS and SPSS, and SAS programs to merge the files. The NIS-Trends CD-ROMs do not include the NIS Core files, which must be obtained separately from the HCUP Central Distributor.

There is one NIS-Trends data file for each year from 1988 to 2002. No supplemental files were created for the 2003 and 2004 NIS because these years served as the base comparison. The 1988-2002 NIS-Trends files are appropriate for use in conjunction with the NIS data files that are available for purchase through the HCUP Central Distributor.

The NIS-Trends Files are provided in fixed-width ASCII files. The files require a statistical software package such as SAS or SPSS to use for analytic purposes. Load programs for SAS and SPSS are provided.

The User Guide for the NIS-Trends Files contains:

• A more detailed description of the files
• Information on data elements
• Instructions for SAS and non-SAS users.

Downloading Information

Web Browser Download: Your browser may support loading the User Guides from this Web page. To download the User Guides from this Web page, click on the following links with the right mouse button and select "Save Link As" (Netscape) or "Save Target As" (Internet Explorer). After saving a file, find it by using Windows® Explorer (Windows® 98/95/NT) or File Manager (Windows® 3.x), and then open the file by double-clicking on it.

• User Guide for the NIS Trends Supplemental Files (PDF file, 84 KB)

HCUP NIS-Trends Files are available from the HCUP Central Distributor. These files are free of charge. Contact the HCUP Central Distributor to obtain your own copy of these files.

The following links include file specifications for the NIS Trends Supplemental files including the dataset name, number of observations, and record layout. Documents are provided in ASCII text format. The amount of time it takes to access a document depends on your machine, browser and Internet connection.

• 1988
• 1989
• 1990
• 1991
• 1992
• 1993
• 1994
• 1995
• 1996
• 1997
• 1998
• 1999
• 2000
• 2001
• 2002