National Hospital Discharge Survey (NHDS)

Session Overview NHDS: Overview Carol DeFrances, Ph.D. Analytic Issues Jean Kozak, Ph.D. Examples of Research Marni Hall, Ph.D. Accessing Data Maria Owings, Ph.D. New Directions Bob Pokras

Overview of the National Hospital Discharge Survey (NHDS) Carol DeFrances, Ph.D.

NHDS Survey Years Conducted annually 1965-present: –Latest data available: 2002 –2003 will be available this Winter

NHDS Survey Design National probability sample: –Short stay non-Federal hospitals Three stage design: 1. Geographic units 2. Hospital 3. Discharge

More Information on NHDS Design and Operations NCHS Publications: Series 1, No. 39 “Design and Operation of the National Hospital Discharge Survey: 1988 Redesign”

NHDS Sample Size Hospitals: –About 500 hospitals sampled per year Discharges: –Over 300,000 sampled per year

NHDS Data Collection Manual hospitals - 60% Automated hospitals - 40%

NHDS Manual Data Collection NCHS – Statistical Design Census Bureau – Field Work Contractor – Coding and Data Entry

NHDS Automated Data Collection Electronic files obtained from: –States –Commercial firms –Individual hospitals

NHDS Data Processing NCHS: –Editing –Estimation

NHDS Estimation Weight: –Inverse of the probability of selection –Adjustments for non-response –Population weighting ratio adjustment

Health Insurance Portability and Accountability Act (HIPAA)

Variables on NHDS Public Use Data Files

Patient Data Age Sex Race Expected source of payment Discharge status Marital status

Hospital Characteristics Geographic region Bed size Ownership

Medical Data Diagnoses and procedures International Classification of Diseases, 9 th Revision, Clinical Modification (ICD-9-CM)

Additional Variables Days of care Month of discharge DRG Weight

New Variables for NHDS Available beginning in the 2001 NHDS: - Source of Admission - Type of Admission

National Survey of Ambulatory Surgery (NSAS) Survey Years: Annually Collected data on ambulatory (outpatient) surgery in the U.S.

NSAS Design National probability sample –Short stay non-Federal hospitals (418) –Freestanding ambulatory surgery centers (333) Sample size: –120,000 sampled visits per year

More Information on NSAS Design and Operations Survey Design and Operations: NCHS Publications: Series 1, No. 37 “Plan and Operation of the National Survey of Ambulatory Surgery”

Additional Variables Collected for NSAS Hospital vs. freestanding center Type of anesthesia Anesthesia provider

Analytic Issues Lola Jean Kozak, Ph.D.

Topics Utilization measures Medical coding system Statistical issues

NHDS provides data on hospitalizations not people

Measures Include: Discharges Days of care Average length of stay Diagnoses Surgeries/procedures

Discharges Include deaths Include transfers to other hospitals or long- term care facilities Do not usually include newborn infants

Days of Care Total number of days discharged patients spend in the hospital All stays are counted as at least 1 day. The admission day is counted, but not the discharge day The number of days divided by the number of discharges is the average length of stay.

Diagnoses Disease, injury or other reason for hospitalization Coded according to US adaptations of the International Classification of Diseases (ICD-9-CM)

Diagnoses Principal diagnosis: chiefly responsible for hospitalization First-listed diagnosis: principal if specified, otherwise one listed first

Diagnoses All-listed: total number of times diagnoses appears on record Any-listed: discharges with diagnosis in any position on record

Hospital discharges with fractures, 2002 Principal or first listed Any listedAll listed 995,000 1,387,000 1,609,000

Surgery/Procedures Surgical (appendectomy) Diagnostic (spinal tap) Therapeutic (chemotherapy) procedures Coded according to US adaptations of the International Classification of Diseases

NHDS provides data on inpatient procedures not total procedures

Versions of the International Classification of Diseases 8 th revision used th revision used th revision for use in future

8 th Revision Some codes different than in 9 th Revision Did not use E-codes Made modifications in coding to accommodate available data

9 th Revision Addenda added annually since 1986 Codes added, deleted, expanded, and revised Lists of changes available in annual summary reports, file documentation

Weights Must use weighted data to obtain unbiased national estimates. Each record has a weight Sum the weights of the records

Reliability To be reliable, estimates must be based on at least 30 records. And have a relative standard error of less than 30 percent. Estimates based on records should be used with caution.

Standard Errors Some standard errors are in Advance Data summaries Generalized error curves are in the Series 13 Annual Summaries and data documentation Use SUDAAN for specific standard errors - need access to confidential data

Examples of Research Using the National Hospital Discharge Survey Marni Hall, Ph.D.

Average length of hospital stay by age, and over All ages Under 15

Percent distribution of hospital inpatients by age and over < 15

Hospital Transfers to Long Term Care Facilities in the 1990’s Jean Kozak Long-Term Care Interface – June 2002

Transfers to long-term care, Number in Millions 1.6 Million 2.8 Million

Average hospital stay for long-term transfers, days 8.3 days

Examples of health services research: Long-stay patients in short-stay hospitals AcademyHealth Annual Meeting Presentation - Marni Hall and Maria Owings - June, 2003 Admit source and type NAHDO Annual Meeting Presentation - Maria Owings and Marni Hall - December 2003 Differences in length of stay in Veterans Health Administration and NHDS hospitals Medical Care - GE Rosenthal et al. - August 2003

Common NHDS Research Topics: Deliveries –Type of birth, e.g. cesarean section –Obstetrical procedures –Length of stay

U.S. Trends in Obstetric Procedures, Jean Kozak and Julie Weeks Birth – September 2002

Rate of cesarean sections,

Rate of vaginal birth after cesarean section,

Common NHDS Research Topics (con’d): Newborns –Premature –Sick/well – common diagnoses –Length of stay in hospital

Average length of stay for newborns, days 3.2 days

Recent diagnoses studied Heart failure Atrial fibrillation Arthritis Pneumonia Mental disorders in children Sepsis

Rate of hospitalization for congestive heart failure for those 65 and over,

Recent procedures studied: Hip replacements Knee replacements Coronary artery revascularization procedures Cervical diskectomy

Rate of knee replacement for inpatients 65 years and older,

Example of trend analyses related to public health Chartbook on Trends in Injury Hospitalizations United States, Melissa Heinen, Marni Hall, Manon Boudreault, Lois Fingerhut NCHS Publication Available in the Fall of 2004

Rate of hospitalization for hip fracture for females 65 and over, Data are plotted on the log scale and over

Other Public Health/ Medical Care Research Diabetes Asthma Obesity Hypertension Chronic Obstructive Pulmonary Disease (COPD)

Other publications using NHDS trend data: Health Care in America. Trends in Utilization, Health United States, Healthy People

For more information see: Internet Resources: Hospital Discharge and Ambulatory Surgery Data (handout)

Accessing Data from the National Hospital Discharge Survey Maria Owings, Ph.D.

What type of data are available?  Publications, including annual reports  Data tabulations on selected topics  Public-use data files (micro-data)

How Can I Obtain Data from the National Hospital Discharge Survey?  Go to the Hospital Discharge and Ambulatory Surgery homepage on the Web:  Telephone the Hospital Care Statistics Branch:  Contact NCHS Information Dissemination Staff NCHS (toll free)  Send an to:

Annual Publications from Hospital Care Statistics Branch  ADVANCE DATA reports: –Provide early release of NHDS data –Are very general and usually short – 2002:  VITAL AND HEALTH STATISTICS Series 13 reports, e.g. Annual Summary and Detailed Reports –Provide more comprehensive statistics on utilization –Contain detailed tables of diagnoses and procedures –2001: sr13_156.pdf

Navigating the NCHS Website  Several avenues are available to find data and reports on NHDS and NSAS  Know what you are looking for, e.g.  Microdata files & documentation  Published reports & tabulations  Follow links – many lead to the same place

What to Know to Access Data and Publications on the Web  Publications, data tables, and data file documentation are in Adobe Acrobat PDF format.  Require use of the free Adobe Acrobat Reader software, available for download at  Data files are in ASCII format and must be downloaded via FTP server  After downloading, files must be “unzipped” using WINZIP or other data extraction software, available for free

Links from the NCHS Homepage:  Surveys & Data Collection Systems  National Health Care Survey, e.g. NHDS & NSAS  Publications & Information Products  Published reports & Data Warehouse  Micro-data Access  Public Use Data Files & Documentation

NHDS & NSAS Homepage  nhds.htm provides links to all aspects of survey design, public use data, and dissemination products, including  Survey Description & Methodology  New Releases & Fact Sheets  NCHS Health E-Stats  Data Highlights & Selected Tables  Publications: reports and journal articles  Public Use Data Files (microdata)

Links to NHDS and NSAS Publications on the Web  listpubs.htm Lists annual publications and special topic reports by name and number (back to 1990 only)  Lists electronic products available for entire Center, including NHDS & NSAS products  AD & Series 13 reports cataloged by number, not name (some back to 1960’s)  Links to Data Warehouse

Data Warehouse  Provides links by topic area for all NCHS products (not just NHDS & NSAS), including  Public Use Files & Documentation  Published Reports, by type e.g. Advance Data, Vital and Health Statistics Series 13, etc (need to know report number)  ICD-9-CM coding index  ftpdata.htm [ FTP server ]

Public-Use Files Available on the Web  Data and documentation available for free from the NCHS website –NHDS: 1996 through 2002 –NSAS: 1994, 1995, 1996  Files are “raw” ASCII data that require the use of standard statistical software packages, such as SAS, SPSS, Stata, etc.

What to Know to Access Public-Use Files on the Web  Downloadable public-use data files are “zipped” for a speedier download  “Unzip” these files with –WinZip ( –PKunzip (  Data file documentation is available in PDF format

Public-Use Files Available on CD-ROM  Single year files available for some years -- From NCHS, years 1990, 1994 to From NTIS, years 1970 to 1998  Two separate multi-year files containing – data years (ICD-9-CM coding) – data years (ICD-8 coding) IMPORTANT: DRGs are available on single year files only. Multi-year files do NOT have DRGs.

How to Get PU Files on CD-ROM  FREE from NCHS by contacting –NCHS Information Dissemination Staff : INFO or NCHS –Hospital Care Statistics Branch:  Purchased from National Technical Information Service (NTIS) * – phone or (703) – online at * Annual files for single years prior to 1994 can only be obtained from NTIS (not available from NCHS)

ICD-9-CM  For full-text, addenda, and conversion tables of ICD-9-CM, see  Full-text ICD-9-CM documents are RTF (Rich Text Format) files and can be handled with any word processing package.  Addenda and conversion tables are PDF documents.

Restricted Data in NHDS  HCSB maintains confidential information in files which are not publicly disseminated  Restricted data pose disclosure risks to survey respondents  These data are available to researchers through the NCHS Research Data Center (RDC) 

Through the RDC Researchers Can Use:  Confidential files for NHDS and NSAS variance estimation  NHDS and NSAS analytic files that have been linked with outside data sources

Confidential Variables Available Only on Restricted Files  ZIPCODE for residence of discharged patient  ZIPCODE for hospital  STATE/COUNTY FIPS CODE for both patient and hospital  AHA ID for hospital  DESIGN VARIABLES needed to run SUDAAN ************************************** NOTE: Identifiers such as patient name, address, and SSN are not collected in the NHDS

NHDS can be linked with other files  NHDS + American Hospital Association (AHA)  NHDS + Area Resource File (ARF)  Linkage is with contextual NOT personal / demographic information  Contextual data include –Hospital characteristics, services (AHA) –County level information (ARF)

Beyond 20/20 Browser  ng/howto.htm#browser2 ng/howto.htm#browser2  Database providing up-to-date information on national trends and key variables that depict the health status of older Americans  Data for persons 45 years old and over by sex and race

NHDS or NSAS Questions? Phone: Fax:

New Directions National Hospital Discharge Survey Bob Pokras

New Directions Internet Data –Beyond 20/20 –Improved internet links Linked files

New Directions Clinical data Evaluation of drugs in the NHDS

NSAS and NHDS NSAS status NHDS status

NHDS and NSAS Carol DeFrances Jean Kozak Marni Hall Maria Owings Bob Pokras