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National Hospital Discharge Survey(NHDS)
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Center for Health Statistics
U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICESCenters for Disease Control and PreventionNational Center for Health Statistics
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Session OverviewNHDS: Overview
Carol DeFrances, Ph.D.
Analytic IssuesJean Kozak, Ph.D.
Examples of ResearchMarni Hall, Ph.D.
Accessing DataMaria Owings, Ph.D.
New DirectionsBob Pokras
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Overview of the National Hospital Discharge Survey
(NHDS)
Carol DeFrances, Ph.D.
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NHDS Survey Years
• Conducted annually 1965-present:
– Latest data available: 2002
– 2003 will be available this Winter
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NHDS Survey Design
• National probability sample:– Short stay non-Federal hospitals
• Three stage design:
1. Geographic units2. Hospital3. Discharge
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More Information on NHDS Design and Operations
• NCHS Publications: Series 1, No. 39
“Design and Operation of the National Hospital Discharge Survey: 1988 Redesign”
http://www.cdc.gov/nchs/data/series/sr_01/sr01_039.pdf
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NHDS Sample Size
• Hospitals:
– About 500 hospitals sampled per year
• Discharges:
– Over 300,000 sampled per year
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NHDS Data Collection
• Manual hospitals - 60%
• Automated hospitals - 40%
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NHDS Manual Data Collection
• NCHS – Statistical Design
• Census Bureau – Field Work
• Contractor – Coding and Data Entry
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NHDS Automated Data Collection
• Electronic files obtained from:
– States
– Commercial firms
– Individual hospitals
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NHDS Data Processing
• NCHS:
– Editing
– Estimation
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NHDS Estimation
• Weight:
– Inverse of the probability of selection
– Adjustments for non-response
– Population weighting ratio adjustment
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Health Insurance Portability and Accountability Act (HIPAA)
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Variables on
NHDS Public Use Data Files
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Patient Data
• Age
• Sex
• Race
• Expected source of payment
• Discharge status
• Marital status
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Hospital Characteristics
• Geographic region
• Bed size
• Ownership
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Medical Data
• Diagnoses and procedures
• International Classification of Diseases, 9th Revision, Clinical Modification (ICD-9-CM)
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Additional Variables
• Days of care
• Month of discharge
• DRG
• Weight
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New Variables for NHDS
Available beginning in the 2001 NHDS:
- Source of Admission
- Type of Admission
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National Survey of Ambulatory Surgery (NSAS)
• Survey Years: Annually 1994-1996
• Collected data on ambulatory (outpatient)
surgery in the U.S.
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NSAS Design
• National probability sample
– Short stay non-Federal hospitals (418)
– Freestanding ambulatory surgery centers (333)
• Sample size:
– 120,000 sampled visits per year
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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”
http://www.cdc.gov/nchs/data/series/sr_01/sr01_037.pdf
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Additional Variables Collected for NSAS
• Hospital vs. freestanding center
• Type of anesthesia
• Anesthesia provider
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Analytic Issues
Lola Jean Kozak, Ph.D.
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Topics
• Utilization measures
• Medical coding system
• Statistical issues
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NHDS provides data on
hospitalizations
not people
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Measures Include:
• Discharges
• Days of care
• Average length of stay
• Diagnoses
• Surgeries/procedures
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Discharges
• Include deaths
• Include transfers to other hospitals or long-term care facilities
• Do not usually include newborn infants
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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.
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Diagnoses
• Disease, injury or other reason for hospitalization
• Coded according to US adaptations of the
International Classification of Diseases (ICD-9-CM)
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Diagnoses
• Principal diagnosis: chiefly responsible for hospitalization
• First-listed diagnosis: principal if specified, otherwise one listed first
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Diagnoses
• All-listed: total number of times diagnoses appears on record
• Any-listed: discharges with diagnosis in any position on record
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Hospital discharges with fractures, 2002
Principal or first listed
Any listed All listed
995,000
1,387,000
1,609,000
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Surgery/Procedures
• Surgical (appendectomy)• Diagnostic (spinal tap)• Therapeutic (chemotherapy) procedures
• Coded according to US adaptations of the International Classification of Diseases
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NHDS provides data on
inpatient procedures
not total procedures
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Versions of the International Classification of Diseases
• 8th revision used 1970-78
• 9th revision used 1979-2004
• 10th revision for use in future
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8th Revision
• Some codes different than in 9th Revision
• Did not use E-codes
• Made modifications in coding to accommodate available data
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9th Revision
• Addenda added annually since 1986
• Codes added, deleted, expanded, and revised
• Lists of changes available in annual summary reports, file documentation
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Weights
• Must use weighted data to obtain unbiased national estimates.
• Each record has a weight
• Sum the weights of the records
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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 30-59 records should be used with caution.
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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
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Examples of Research Using the National Hospital Discharge
Survey
Marni Hall, Ph.D.
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Average length of hospital stay by age, 1970-2001
0
2
4
6
8
10
12
14
1970 1975 1980 1985 1990 1995 2000 2001
Day
s
65 and over
45-64
All ages
15-44
Under 15
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Percent distribution of hospital inpatients by age
0
20
40
60
80
100
Per
cent
1970 1980 1990 2002
65 and over
45-64
15-44
< 15
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Hospital Transfers to Long Term Care Facilities in the 1990’s
Jean Kozak
Long-Term Care Interface – June 2002
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Transfers to long-term care,1990-1999
Num
ber
in M
illi
ons
0
0.5
1
1.5
2
2.5
3
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
1.6 Million
2.8 Million
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Average hospital stay for long-term transfers, 1990-1999
0
2
4
6
8
10
12
14
1990 1991 1992 1993 1994 1995 1996 1997 1998 1999
Day
s
12.8 days
8.3 days
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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
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Common NHDS Research Topics:
• Deliveries
– Type of birth, e.g. cesarean section
– Obstetrical procedures
– Length of stay
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U.S. Trends in Obstetric Procedures, 1990-2000
Jean Kozak and Julie Weeks
Birth – September 2002
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Rate of cesarean sections,1980-2002
0
6
12
18
24
30
36
1980 1985 1990 1995 2000 2002
Rat
e pe
r 10
0 de
live
ries
16.5
26.8
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Rate of vaginal birth after cesarean section, 1990-2002
0
6
12
18
24
30
36
1985 1990 1995 2000 2002
Rat
e pe
r 10
0 de
live
ries
15.8
6.6
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Common NHDS Research Topics (con’d):
• Newborns– Premature– Sick/well – common diagnoses– Length of stay in hospital
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Average length of stay for newborns,1980-2002
0
1
2
3
4
5
1980 1985 1990 1995 2000 2002
Day
s
4.3 days
3.2 days
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Recent diagnoses studied
Heart failureAtrial fibrillation
ArthritisPneumonia
Mental disorders in childrenSepsis
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Rate of hospitalization for congestive heart failure for those 65 and over,
1980-2002
0
50
100
150
200
250
1980 1985 1990 1995 2000 2002
Rat
e pe
r 10
,000
pop
ulat
ion
133.4
201.4
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Recent procedures studied:
Hip replacementsKnee replacements
Coronary artery revascularization procedures
Cervical diskectomy
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Rate of knee replacement for inpatients 65 years and older, 1991-2002
0
10
20
30
40
50
60
70
1990 1995 2000
Rat
e pe
r 10
,000
pop
ulat
ion
38.2
67.6
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Example of trend analyses related to public health
Chartbook on Trends in Injury Hospitalizations United States, 1979-2001
Melissa Heinen, Marni Hall, Manon Boudreault, Lois Fingerhut
NCHS Publication Available in the Fall of 2004
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Rate of hospitalization for hip fracture for females 65 and over, 1980-2001
1
10
100
1000
1980 1985 1990 1995 2000 2001
Dis
char
ges
per
10,0
00 p
opul
atio
n
Data are plotted on the log scale.
65-74
75-84
85 and over
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Other Public Health/Medical Care Research
DiabetesAsthmaObesity
HypertensionChronic Obstructive Pulmonary
Disease (COPD)
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Other publications using NHDS trend data:
Health Care in America. Trends in Utilization, 2004http://www.cdc.gov/nchs/pressroom/04facts/healthcare.htm
Health United States, 2003http://www.cdc.gov/nchs/hus.htm
Healthy People 2010http://www.cdc.gov/nchs/hphome.htm
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For more information see:
Internet Resources: Hospital Discharge and Ambulatory
Surgery Data (handout)
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Accessing Data from the National Hospital Discharge Survey
Maria Owings, Ph.D.
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What type of data are available?
Publications, including annual reports
Data tabulations on selected topics
Public-use data files (micro-data)
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How Can I Obtain Data from theNational Hospital Discharge Survey?
Go to the Hospital Discharge and Ambulatory Surgery homepage on the Web: www.cdc.gov/nchs/about/major/hdasd/nhds.htm
Telephone the Hospital Care Statistics Branch: 301-458-4321
Contact NCHS Information Dissemination Staff 1-866-441-NCHS (toll free)
Send an email to: [email protected]
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Annual Publications fromHospital Care Statistics Branch
ADVANCE DATA reports:– Provide early release of NHDS data – Are very general and usually short– 2002: http://www.cdc.gov/nchs/data/ad/ad342.pdf
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: http://www.cdc.gov/nchs/data/series/sr_13/ sr13_156.pdf
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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
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What to Know to Access Data and Publications on the WebPublications, 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 www.adobe.com
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
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Links from the NCHS Homepage:www.cdc.gov/nchs
Surveys & Data Collection Systems National Health Care Survey, e.g.
NHDS & NSASPublications & Information Products
Published reports & Data WarehouseMicro-data Access
Public Use Data Files & Documentation
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NHDS & NSAS Homepagehttp://www.cdc.gov/nchs/about/major/hdasd/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)
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Links to NHDS and NSAS Publications on the Web
http://www.cdc.gov/nchs/about/major/hdasd/listpubs.htm
Lists annual publications and special topic reports by name and number (back to 1990 only)
http://www.cdc.gov/nchs/products.htm 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
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Data Warehouse http://www.cdc.gov/nchs/datawh.htm
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
http://www.cdc.gov/nchs/datawh/ftpserv/ftpdata/ ftpdata.htm [ FTP server ]
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Public-Use Files Available on the Web
Data and documentation available for free from the NCHS website
–NHDS: 1996 through 2002
–NSAS: 1994, 1995, 1996Files are “raw” ASCII data that require the
use of standard statistical software packages, such as SAS, SPSS, Stata, etc.
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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 (www.winzip.com)
–PKunzip (www.pkware.com)Data file documentation is available in
PDF format
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Public-Use Files Available on CD-ROM
Single year files available for some years -- From NCHS, years 1990, 1994 to 1998-- From NTIS, years 1970 to 1998
Two separate multi-year files containing – 1979-2002 data years (ICD-9-CM coding)– 1970-1978 data years (ICD-8 coding)
IMPORTANT: DRGs are available on single year files only. Multi-year files do NOT have DRGs.
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How to Get PU Files on CD-ROM FREE from NCHS by contacting
– NCHS Information Dissemination Staff :
301-458-INFO or 1-866-441-NCHS
– Hospital Care Statistics Branch: 301-458-4321 Purchased from National Technical Information
Service (NTIS) *
– phone 1-800-553-6847 or (703) 605-6000
– online at www.ntis.gov
* Annual files for single years prior to 1994 can only be obtained from NTIS (not available from NCHS)
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ICD-9-CM
For full-text, addenda, and conversion tables of ICD-9-CM, see www.cdc.gov/nchs/icd9.htm
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.
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Restricted Data in NHDS HCSB maintains confidential information in
files which are not publicly disseminatedRestricted data pose disclosure risks to
survey respondentsThese data are available to researchers
through the NCHS Research Data Center (RDC)
http://www.cdc.gov/nchs/r&d/rdc.htm
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Through the RDCResearchers Can Use:
Confidential files for NHDS and NSAS variance estimation
NHDS and NSAS analytic files that have been linked with outside data sources
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Confidential Variables Available Only on Restricted Files
ZIPCODE for residence of discharged patientZIPCODE for hospitalSTATE/COUNTY FIPS CODE for both patient
and hospitalAHA ID for hospitalDESIGN VARIABLES needed to run SUDAAN
************************************** NOTE: Identifiers such as patient name, address,
and SSN are not collected in the NHDS
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NHDS can be linked with other files
NHDS + American Hospital Association (AHA)NHDS + Area Resource File (ARF)Linkage is with contextual NOT personal /
demographic informationContextual data include
– Hospital characteristics, services (AHA)
– County level information (ARF)
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Beyond 20/20 Browser
http://www.cdc.gov/nchs/about/otheract/aging/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
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NHDS or NSAS Questions?
Phone: 301-458-4321
Fax: 301-458-4032
Email: [email protected]
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New Directions National Hospital Discharge Survey
Bob Pokras
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New Directions
• Internet Data– Beyond 20/20– Improved internet links
• Linked files
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New Directions
• Clinical data
• Evaluation of drugs in the NHDS
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NSAS and NHDS
• NSAS status
• NHDS status
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NHDS and NSAS
Carol DeFrances
Jean Kozak
Marni Hall
Maria Owings
Bob Pokras