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

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

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 units2. Hospital3. 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”

http://www.cdc.gov/nchs/data/series/sr_01/sr01_039.pdf

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, 9th 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 1994-1996

• 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”

http://www.cdc.gov/nchs/data/series/sr_01/sr01_037.pdf

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 listed All 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

• 8th revision used 1970-78

• 9th revision used 1979-2004

• 10th revision for use in future

8th Revision

• Some codes different than in 9th Revision

• Did not use E-codes

• Made modifications in coding to accommodate available data

9th 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 30-59 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, 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

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

Hospital Transfers to Long Term Care Facilities in the 1990’s

Jean Kozak

Long-Term Care Interface – June 2002

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

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

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, 1990-2000

Jean Kozak and Julie Weeks

Birth – September 2002

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

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

Common NHDS Research Topics (con’d):

• Newborns– Premature– Sick/well – common diagnoses– Length of stay in hospital

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

Recent diagnoses studied

Heart failureAtrial fibrillation

ArthritisPneumonia

Mental disorders in childrenSepsis

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

Recent procedures studied:

Hip replacementsKnee replacements

Coronary artery revascularization procedures

Cervical diskectomy

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

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

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

Other Public Health/Medical Care Research

DiabetesAsthmaObesity

HypertensionChronic Obstructive Pulmonary

Disease (COPD)

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

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 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: NHDS@cdc.gov

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

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 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

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

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)

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

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 ]

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.

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

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.

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)

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.

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

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

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

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)

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

NHDS or NSAS Questions?

Phone: 301-458-4321

Fax: 301-458-4032

Email: NHDS@cdc.gov

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