Design and Operation of the

National Hospital Discharge

Survey: 1988 Redesign

Series 1:

Programs and Collection

Procedures

No. 39

Hyattsville, Maryland

December 2000

DHHS Publication No. (PHS) 2001-1315

Vital and

Health Statistics

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES

Centers for Disease Control and Prevention

National Center for Health Statistics
Copyright Information

All material appearing in this report is in the public domain and may be

reproduced or copied without permission; citation as to source, however, is

appreciated.

Suggested Citation

Dennison C, Pokras R. Design and operation of the National Hospital Discharge

Survey: 1988 redesign. Vital Health Stat 1(39). 2000.

Library of Congress-in-Publication Data

Dennison, Charles F.

Design and operation of the National Hospital Discharge Survey / [by

Charles Dennison and Robert Pokras].

p. cm.—(Vital and health statistics. Series 1, Programs and collection

procedures ; no. 39) (DHHS publication ; no. (PHS) 2001-1315)

‘‘October 2000.’’

Includes bibliographical references.

ISBN 0-8406-0565-X

1. National Hospital Discharge Survey (U.S.) 2. Hospital utilization—United

States—Statistics. 3. Medical care surveys—United States 4. Health

surveys—United States. I. Pokras, Robert. II. National Center for Health

Statistics (U.S.) III. Title IV. Series. V . Series: DHHS publication ; no. (PHS)

2001-1315.

RA409.U44 no. 39

[RA407.3]

362.1’07’23 s—dc21

[362.1’1’0973] 00-064743

For sale by the U.S. Government Printing Office

Superintendent of Documents

Mail Stop: SSOP

Washington, DC 20402-9328

Printed on acid-free paper.
National Center for Health Statistics

Edward J. Sondik, Ph.D., Director

Jack R. Anderson, Deputy Director

Jack R. Anderson, Acting Associate Director for

International Statistics

Jennifer H. Madans, Ph.D., Associate Director for Science

Lester R. Curtin, Ph.D., Acting Associate Director for

Research and Methodology

Jennifer H. Madans, Ph.D., Acting Associate Director for

Analysis, Epidemiology, and Health Promotion

P. Douglas Williams, Acting Associate Director for Data

Standards, Program Development, and Extramural Programs

Edward L. Hunter, Associate Director for Planning, Budget,

and Legislation

Jennifer H. Madans, Ph.D., Acting Associate Director for

Vital and Health Statistics Systems

Douglas L. Zinn, Acting Associate Director for

Management

Charles J. Rothwell, Associate Director for Information

Technology and Services

Division of Health Care Statistics

Linda Demlo, Ph.D., Director

Thomas McLemore, Deputy Director

Irma Arispe, Ph.D., Associate Director for Science

Robert Pokras, Chief, Hospital Care Statistics Branch
Contents

Abstract ................................................................................................. 1

Introduction ............................................................................................. 1

Background .............................................................................................. 1

Sample Design............................................................................................ 2

First Stage Sampling—Primary Sampling Units .............................................................. 2

Second Stage Sampling—Hospitals ......................................................................... 2

Third Stage Sampling—Discharges ......................................................................... 3

Confidentiality ........................................................................................... 4

Survey Operations ........................................................................................ 4

Manual Data Collection and Processing ..................................................................... 4

Automated Data Collection and Processing ................................................................... 6

Estimation Procedures ..................................................................................... 9

Inflation by Reciprocals of Probabilities of Selection .......................................................... 9

Adjustment for Nonresponse .............................................................................. 9

Population Weighting Ratio Adjustment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Reliability of Estimates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Estimation of Standard Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Standard Error Approximations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Relative Standard Error for Estimates of Percents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Nonsampling Errors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Data Dissemination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Text Tables

A. Definition of noncertainty hospital specialty-size groups used as secondary strata in the National Hospital Discharge

Survey sample design, 1988 sample design .............................................................. 3

B. Number of hospitals in the National Hospital Discharge Survey sample, number of in-scope and responding sample

hospitals, response rates, and number of abstracts collected: United States, 1988–97 ............................ 3

C. Estimated parameters for approximate relative standard error equations by selected characteristics: National Hospital

Discharge Survey, 1997 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Appendixes

I. Legislative Authorization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

II. Induction Letter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

III. American Hospital Association Endorsement Letter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

IV. Confidentiality Letter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

V. Hospital Interview Questionnaire (HDS-11) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

VI. Medical Abstract—National Hospital Discharge Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

iii
VII. Sample Selection Sheet (HDS-5) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

VIII. Statement of Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

IX. Abstract Service Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

X. Transmittal Notice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

XI. Automated File Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

XII. Information Request Letter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41

XIII. Definitions of Terms Related to Survey . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

iv
The National Hospital Discharge

Survey (NHDS), a national probability

sample survey of discharges from

non-Federal hospitals, began in 1965

and has been conducted annually since

then. The original design of NHDS was

in place through 1987. This report

provides information about the survey

design, instruments, data collection

procedures, and survey methodology

used for NHDS since the

implementation of its redesign in 1988.

Keywords: inpatients, hospital,

hospital discharges, National

Hospital Discharge Survey

Design and Operation of the

National Hospital Discharge

Survey: 1988 Redesign

by Charles Dennison and Robert Pokras, M.A., Division of Health

Care Statistics

Introduction

I

n 1965 the National Center for

Health Statistics (NCHS) initiated

the National Hospital Discharge

Survey (NHDS) to collect and

disseminate data on inpatient utilization

of short-stay non-Federal hospitals in

the United States and District of

Columbia. The importance of measuring

inpatient care made NHDS the first

survey of medical care delivery

conducted by the NCHS (1,2) and

inpatient care continues to play a major

role in health care delivery (3). The

NHDS has been conducted annually

since its inception.

Authority for the NHDS derived

from the National Health Survey Act of

1956 (Public Law 84–652) and it has

continued under various acts of

Congress, principally under Section

306(b)(1)(F) (appendix I) of the Public

Health Service Act (42 USC 242k) and

its amendments to collect data

concerning the public’s use of health

care services.

The NHDS was conducted under

the same design from 1965 through

1987. A previous report describes the

development and design of the NHDS

during this period (4). A redesign for the

survey was implemented in 1988. This

report describes the design and

operation of the NHDS, which began

with the 1988 survey year and major

changes to NHDS resulting from the

new design. These changes include the

use of a 3-stage sample design, the use

of automated data, and the ability to use

SUDAAN to estimate variances.

Background

The impetus to redesign the NHDS

was to select a new independent

national probability sample of

hospitals. The initial sample of hospitals

for NHDS was used for the 23-year

period 1965–87. The redesign focused

on improving the efficiency and analytic

capability of the survey by 1) linking

the NHDS to the design of NCHS’s

National Health Interview Survey

(NHIS), 2) incorporating hospital

discharge data available in electronic

form, and 3) allowing the use of

existing statistical software to estimate

variances.

The redesign included linkage with

the design of NHIS (5), the principal

source of information on the health of

the civilian noninstitutionalized

population of the United States. Before

1988 the NHDS used a two-stage

sample design (a sample of hospitals

and a sample of records within

hospitals); the redesign included a third

stage prior to sampling hospitals, the

selection of geographic primary

sampling units (PSU’s). The redesign

used a sub-sample of PSU’s selected for

the 1985–94 NHIS. This modification

was intended to enhance the analytic

capabilities of both surveys and to

reduce the field costs of the surveys by

conducting them in the same geographic

areas.

Page 1
The redesign also took into account

the increasing availability of discharge

data in electronic (automated) form.

Before the redesign, the NHDS

depended almost entirely on manual

sampling and abstraction of information

from medical records. The exception to

this was that automated data were

obtained for about 75 hospitals annually

during the period 1985–87. With the

implementation of the new design in

1988, information on the characteristics

of a majority of discharges in NHDS

were obtained from existing hospital

discharge data bases. However, a

majority of hospitals provide data by

means of manual sampling and

abstraction. This seeming contradiction

is explained by the fact that, as part of

the redesign, more records are sampled

from hospitals providing automated data

than are sampled from hospitals in

which data are manually abstracted from

medical records. The target sample size

is 250 discharges from manual hospitals

and 2,000 discharges from automated

system hospitals.

Also, the new redesign allows the

use of available statistical software to

estimate variances for estimates. Before

1988 NCHS used a program written at

NCHS specifically for the NHDS to

calculate variances. The redesign allows

the use of SESUDAAN and SUDAAN

(6, 7) for this purpose. This is more

efficient for data dissemination and it

allows researchers to more readily

generate variances for specific areas of

interest.

There are a number of less

significant differences between the

original and new designs that have been

documented (8,9). These include a

different source as the operational

definition of the hospital universe and

minor differences in the statical design

of the survey. The changes introduced

do not compromise the ability to

conduct trend analysis; however, the

addition of clustering introduced by

including a third stage of sampling

(PSU’s) reduced the precision of

estimates.

Sample Design

The NHDS is based on a national

probability sample of discharges

from noninstitutional hospitals

exclusive of Federal, military, and

Department of Veterans Affairs

hospitals, located in the 50 States and

the District of Columbia. Only

short-stay hospitals (hospitals with an

average length of stay for all patients of

less than 30 days) or those whose

speciality is general (medical or

surgical) or children’s general regardless

of length of stay are included in the

survey. Also, a hospital must have six or

more beds staffed for patient use to be

in scope for the survey. The 1988

NHDS sampling frame consisted of

hospitals that were listed in the April

1987 SMG Hospital Market Database

(10) and that began to accept inpatients

by August 1987.

Given fixed costs, the NHDS is

designed to provide estimates of

inpatient hospital utilization based on

the following priority of objectives:

national aggregate statistics, national

trend statistics, and aggregate statistics

for the four major Census Regions of the

United States. The NHDS uses a

modified three-stage probability design,

the stages are: 1) primary sampling units

(PSU’s); 2) hospitals within PSU’s; and

3) discharges within hospitals. The

modification was that the largest PSU’s

and hospitals were selected with

certainty.

First Stage Sampling—

Primary Sampling Units

The first stage of sampling

consisted of 112 primary sampling units

(PSU’s) that comprised a probability

subsample of PSU’s used in the

1985–94 NHIS. PSU’s are counties,

groups of counties, county equivalents

(such as parishes or independent cities),

or towns and townships (for some

PSU’s in New England). The NHDS

sample included with certainty 26 PSU’s

with the largest populations. In addition,

the sample included one-half of the next

26 largest PSU’s, and one PSU from

each of the 73 PSU’s strata formed from

the remaining PSU’s in the NHIS

sample design. Those 73 PSU’s strata

were defined within four geographic

regions and metropolitan statistical area

(MSA) or non-MSA status (MSA was a

metropolitan statistical area defined by

the U.S. Office of Management and

Budget on the basis of the 1980 census).

PSU’s were assigned to strata by using

1980 Census of Population data and a

computer program that minimized the

between-PSU variances for the NHIS

stratification variables. From the 73

strata thus formed, the PSU’s were

selected with probability proportional to

the projected 1985 population. A more

detailed description of the NHIS PSU

sample design has been published (5).

Second Stage

Sampling—Hospitals

The second stage of sampling

consisted of a systematic random sample

of noncertainty hospitals selected from

the sample PSU’s with probability

proportional to their annual number of

discharges. To assure distribution of the

sample across PSU’s and to maximize

the potential for automated data

collection, the noncertainty hospitals

were stratified by region, PSU, and in

the 12 largest PSU’s, by data collection

type (whether the hospital subscribed to

a commercial abstracting service).

Within the strata, the hospitals were

ordered by PSU, whether the hospital

participated in the 1987 NHDS and by

hospital size and speciality as defined in

table A. Finally, hospitals were arrayed

within speciality by their annual number

of discharges. The sampling rates were

such that at least three hospitals were

selected from every PSU containing

three or more eligible hospitals. In

PSU’s with fewer than three hospitals,

all hospitals in the PSU were selected.

The sample design resulted in the

selection of 542 hospitals for the NHDS

in 1988. Of these, 11 hospitals were out

of scope and 109 refused to participate

or did not provide enough data to be

considered responding. This resulted in

422 hospitals participating in the survey,

a response rate of 79.5 percent. Through

a concerted effort to increase the

hospital response rate, this was raised to

Page 2 [ Series 1, No. 39
91.3 percent in 1990 and it did not fall

below 90 percent through 1997. Table B

provides information on hospital

participation for the NHDS from 1988

through 1997.

NCHS conducts several activities to

keep the sample of hospitals in the

NHDS current with the changing

universe of hospitals in the United

States: hospitals in the NHDS sample

that no longer meet eligibility

requirements for the survey are

removed; methods were developed and

implemented for hospitals that merge;

and NCHS samples a ‘‘birth panel’’ of

hospitals every 3 years from all new

hospitals that came into existence since

the previous set of birth panel hospitals

were selected. Research has shown that

adding hospitals from birth panels was

effective in ensuring that estimates from

the survey reflect the changing universe

of hospitals (11).

Third Stage

Sampling—Discharges

At the third stage, a sample of

discharges from each hospital is selected

by a systematic random sampling

technique. For hospitals using the

manual system of data collection,

sampling rates for discharges are

designed to generate samples of

approximately equal numbers regardless

of hospital size. This characteristic of

the design allows efficiencies in field

operations by ensuring that the number

of medical records sampled and

abstracted in the field can be completed

in a single day, thereby avoiding

repeated trips to a hospital by census

personnel (see Manual Data Collection

and Processing). To achieve this

operational goal, discharges are sampled

in inverse proportion to hospital size

with a target of 20–25 discharges

sampled per month.

For hospitals whose data are

collected via the automated system,

discharges are sampled in one of two

methods depending on whether NCHS

receives a sample or a census file of

discharges for the hospital. Some

automated sources prefer to provide a

sample of discharges. For these sources

NCHS provides instructions and

sampling specifications to use terminal

digits of medical records to sample

discharges as described above for

manual data collection. For automated

data that contains all discharges for

hospitals, NCHS samples discharges

after sorting by the first two digits of

the International Classification of

Diseases, Clinical Modification, Ninth

Revision, or ICD–9–CM code (12) of

the first-listed diagnosis, patient age

group at time of admission (under 1

year, 1–14 years, 15–44 years, 45–64

years, 65–74 years, 75–84 years, 85

years and over, and age unknown), sex,

and date of discharge. Discharges are

sampled by starting with a randomly

selected discharge and taking every kth

discharge thereafter.

The third-stage sampling rate is

determined by the hospital’s sampling

stratum and the data collection method

(manual or automated) used to collect

data from the hospital. One percent and

5 percent of discharges in the certainty

hospitals are selected under the manual

and automated systems. Except for

certainty hospitals, the target sample

size is 250 discharges annually from

manual system hospitals, from the

automated system hospitals that had

fewer than 4,000 discharges annually

according to the 1987 sampling frame

data, and from automated hospitals that

provided sample data. Samples of 2,000

discharges are targeted for each of the

remaining noncertainty automated

system hospitals that provide files of all

discharges to NCHS. The sample design

resulted in the selection of 300,464

discharges for the NHDS in 1997.

Table B provides information on the

number of sampled discharges included

in the NHDS from 1988 through 1997.

Table A. Definition of noncertainty hospital specialty-size groups used as secondary

strata in the National Hospital Discharge Survey 1988 sample design

Hospital group Bed size Type of service

Group 1 ................... 6–999 beds Selected specialties1

Group 2 ................... 6–174 beds General (medical and surgical) and other specialties2

Group 3 . . . . . . . . . . . . . . . . . . . 175–349 beds General (medical and surgical) and other specialties2

Group 4 . . . . . . . . . . . . . . . . . . . 350–999 beds General (medical and surgical) and other specialties2

1Includes psychiatry, tuberculosis and other respiratory disease, rehabilitation, chronic disease, mental retardation, alcoholism

and other chemical dependancy, and children’s psychiatry.

2‘‘Other specialties’’ include obstetrics and gynecology: eye, ear, nose and throat; orthopedics; other specialty; children’s general;

children’s tuberculosis and other respiratory disease; children’s eye, ear, nose, and throat; children’s rehabilitation; children’s

orthopedics; children’s chronic disease; and children’s other specialty.

Table B. Number of hospitals in the National Hospital Discharge Survey sample, number of

in-scope and responding sample hospitals, response rates, and number of abstracts

collected: United States, 1988–97

Year

Sample

hospitals

In-scope hospitals

Hospital

response

rate

Discharges

Total sampled

Response type

Total

Manual Automated respondents

Number Percent Number

1988 . . . . . . . . . . . . . . . . . . . . . 542 531 255 167 422 79.5 250,243

1989 . . . . . . . . . . . . . . . . . . . . . 542 526 256 152 408 77.6 233,493

1990 . . . . . . . . . . . . . . . . . . . . . 542 519 299 176 475 91.3 265,556

1991 ..................... 1

528 521 323 161 484 92.9 274,311

1992 . . . . . . . . . . . . . . . . . . . . . 528 514 311 183 494 96.1 274,273

1993 . . . . . . . . . . . . . . . . . . . . . 528 513 303 163 466 90.8 235,411

1994 ..................... 1

525 512 298 180 478 93.4 276,533

1995 . . . . . . . . . . . . . . . . . . . . . 525 508 299 167 466 91.7 262,809

1996 . . . . . . . . . . . . . . . . . . . . . 525 507 299 181 480 94.7 282,008

1997 ..................... 1

513 501 284 187 474 94.6 300,464

1Changes reflect triannual updates to the NHDS hospital universe.

Series 1, No. 39 [ Page 3
Confidentiality

Participation in surveys conducted

by the National Center for Health

Statistics (NCHS) is voluntary,

and information on individuals and/or

facilities is confidential. For the NHDS,

assurance of confidentiality was

provided to all hospitals according to

Section 308(d) of the Public Health

Service Act (42 U.S.C. 242m), which

states that:

‘‘No information, if an

establishment or person supplying

the information or described in it

is identifiable, obtained in the

course of activities undertaken or

supported under section ...306,...

may be used for any purpose other

than the purpose for which it was

supplied unless such establishment

or person has consented (as

determined under regulations of

the Secretary) to its use for such

other purpose and in the case of

information obtained in the course

of health statistical or

epidemiological activities under

section ...306, such information

may not be published or released

in other form if the particular

establishment or person supplying

the information or described in it

is identifiable unless such

establishment or person has

consented (as determined under

regulations of the Secretary) to its

publication or release in other

form.’’

Strict procedures are utilized to

prevent disclosure of confidential data in

survey operations and data

dissemination. Names or other

identifying information for individual

patients are not obtained from the

sampled hospitals. Data received in

electronic form are maintained at the

CDC Atlanta computer processing

center. Under provisions of the DHHS

guidelines for storage of health records,

all original data collected for the survey

are transferred to the Federal Records

Center located in Atlanta, Georgia.

These records are retained for 7 years

before they are destroyed. To prevent

identification of sampled hospitals or

patients from publicly available research

files, variables such as medical record

number, date of birth, admission and

discharge dates, and patient ZIP Code

are not released.

Survey Operations

This section describes the survey

operations for manual and

automated data collection

procedures. With minor exceptions the

survey forms, manuals, and operating

procedures used for manual data

collection during the initial design were

continued with the redesigned survey in

1988. As described in the Introduction,

there were three major factors that

influenced the redesign of the NHDS,

one of which was the use of existing

discharge data in electronic (automated)

form. Data for the NHDS were collected

manually from 1965 through 1984. For

the 3 years, 1985–87, NCHS purchased

discharge data for about 75 hospitals

annually from a contractor. Beginning in

1988 NCHS began purchasing

automated data for approximately 170

hospitals annually.

Manual Data Collection

and Processing

The Bureau of the Census has

served as the agent for data collected

manually in the NHDS since its

inception in 1965. The Census Bureau is

composed of a headquarters and 12

regional offices. In collaboration with

NCHS, Census Headquarters staff

developed the survey operation

procedures; wrote, printed, and

distributed all field manuals and forms

for the NHDS; made modifications to

these documents as variables were

introduced or changed; and, generally

oversaw operations of the manual data

collection. Regional office staff are

responsible for daily operations of the

survey, training new field staff, and

supplying survey forms and materials to

hospital staff.

The major elements of the NHDS

field operations consist of inducting

sampled hospitals into the survey,

sampling discharges, and abstracting

data from medical records. These

functions are described below.

Hospital Induction

Hospital induction is the process of

getting sampled hospitals to participate

in NHDS. As a voluntary survey,

NCHS, through the Census, must obtain

written permission from each sampled

hospital to abstract data from its medical

records. While hospital participation is

the primary purpose of induction, other

important activities are performed.

Hospital induction begins when the

Census regional office mails an

introductory letter (appendix II)

provided by the NCHS to the hospital

administrator or chief executive officer.

Enclosures with this letter include an

information packet containing a fact

sheet about the NHDS, a publication list

and a description of data products

available from the survey, an

endorsement letter from the American

Hospital Association (appendix III), a

recent NHDS publication, and a letter

that addressed confidentiality (appendix

IV).

Approximately 5 days after mailing

the introductory letter, Census staff call

the hospital administrator to arrange an

appointment for an induction interview.

Since part of the interview relates to

information about medical records and

the medical records department, a

representative from the medical records

department (usually the Medical

Records Administrator) is usually

present at this meeting. The functions of

the initial interview are to explain the

purpose of the NHDS, to gain the

hospital’s cooperation in the survey, to

describe the data collection methods

available for survey participation

(described below), to obtain information

about the hospital by completing the

Hospital Interview Questionnaire

(appendix V), to set up sampling and

data collection procedures, and to

distribute manuals and forms.

During induction, a Hospital

Interview Questionnaire is completed.

Information about the facility such as

ownership, service type, bed size, and

average length of stay is collected to

verify the hospital’s eligibility for the

survey. Information about the medical

Page 4 [ Series 1, No. 39
records department, where and how

records are kept and stored, and where

to locate the survey variables in the

medical records is collected to assist in

survey operations. In addition,

reimbursement rates are established for

hospital personnel who work on survey

activities. The level of involvement of

hospital personnel in the NHDS is

determined by the data collection

method. Methods for manual data

collection are described in the next

section.

There was a large scale induction of

hospitals in 1988 as a result of selecting

a new sample of hospitals in the

redesign. Although less frequent,

inductions also take place as

nonresponding hospitals agree to

participate in the survey.

Nonresponding hospitals are contacted

annually in an effort to gain their

participation. Also, hospitals that are

added to the NHDS sample as part of

the universe update (see Statistical

Design) go through the induction

process.

Manual Data Collection

Methods

There were three options for manual

data collection: primary, alternate, and

printout. In the primary method, hospital

personnel in the medical records

department sample discharges for

inclusion in the survey and abstract data

from the sampled medical records onto

the survey form (appendix VI). As the

name implies, this is the preferred

method because hospital staff are more

familiar with their medical records and

data than are Census personnel. In the

primary method hospital staff are given

field manuals, detailed instructions, and

trained by Census personnel to perform

the sampling and abstracting. In 1997

about 40 percent of all manual hospitals

in the NHDS provided data using the

primary method.

The alternate method is used when

hospitals are unwilling or unable to have

their personnel perform the sampling

and abstracting. In this method, the

Census Field Representative selects the

sampled discharges, arranges with the

hospital medical records staff to have

the medical records pulled for

abstracting, and the Field Representative

abstracts the records. Every effort is

made to select experienced Census Field

Representatives who have an

understanding of medical terminology

and are familiar with working with

medical records professionals. Thirty

percent of manual hospitals participated

in this mode of manual data collection

for the 1997 NHDS.

Hospitals also provide data in the

‘‘manual’’ mode by supplying

computerized printouts of information

for sampled discharges. This is

considered manual data collection

because patient information on the

printouts required manual data entry

(see Medical Coding and Data Entry).

Hospitals using this mode provide

definitions for coded variables (that is,

1 = male; 2 = female) to ensure correct

data entry. Computerization of inpatient

data has made printouts more common

in the NHDS; this method of data

collection accounted for about 8 percent

of manual data collection in 1988 rising

to about 30 percent in 1997.

Sampling Discharges

Discharges within hospitals are

selected using systematic random

sampling with the sampling intervals

based on the statistical design of the

survey and specified by NCHS. This is

usually accomplished using daily or

monthly discharge lists and selecting

discharges with specified terminal digits

of medical record numbers. In some

cases an admission number, billing

number, or other patient number is used.

If patient specific numbers useful for

sampling are not available, discharges

are selected by using a random starting

number and then physically counting

through a discharge list and selecting

every kth discharge thereafter. In a few

hospitals discharges are sampled using

the terminal digits of the medical record

numbers on in-house computer files.

Information about sampled

discharges is recorded on a Sample

Listing Sheet (appendix VII). A Sample

Listing Sheet is completed for each

month’s sample of records. It includes

information such as medical record

numbers and dates of discharges that

allowed medical records to be identified

and pulled for abstracting. Sampling

schemes that require a physical count of

discharges (as described above) are kept

continuous by tracking on the Sample

Listing Sheet where the sample selection

process stopped in the previous period.

Medical Record Abstracting

Using the Sample Listing Sheets,

completed medical records are pulled

for abstracting. Records that are not

complete or not available are located at

a later time for abstracting. The NHDS

was designed to sample approximately

20–25 discharges per month per hospital

that allow Census personnel to sample

and abstract 2 months of medical

records in a single day.

Primarily using the medical record

face sheet and discharge summary,

patient information is abstracted onto

the survey form (appendix VI).

Variables collected in the NHDS

conform with the Uniform Hospital

Discharge Data Set (UHDDS) (13,14).

These variables include birth date or

age; sex; race; ethnicity; marital status;

admission, discharge, and surgery dates;

discharge status; patient ZIP Code;

expected source(s) of payment; medical

record number; and information on

diagnoses and procedures. The NHDS

survey methods instruct that, where

possible, narrative information for

diagnoses and procedures be collected,

but in many instances only International

Classification of Diseases, Ninth

Revision, Clinical Modification or

ICD–9–CM (12) codes are available. In

1997 about 30 percent of all manually

abstracted records included only

ICD–9–CM codes for diagnoses and

procedures.

Additional variables are entered on

the abstract form for survey operations.

These included the hospital number (a

number assigned to the hospital for

processing by NCHS) and the HDS

number (a number assigned to the

sampled record for processing by

NCHS).

Medical abstracts and Sample

Listing Sheets are sent to the Census

Regional Offices where forms for each

month are logged in and reviewed for

completeness. This allows Regional

Series 1, No. 39 [ Page 5
Office staff to track survey activities and

ensure that forms were completed

correctly. Monthly shipments of

abstracts and Sampling Listing Sheets

from the Regional Offices are sent to the

NCHS processing center in Research

Triangle Park, North Carolina, for

medical coding and data entry.

Medical Coding and Data

Entry

For the 1965–97 survey years all

materials sent from the Census Regional

Offices were processed by the Division

of Data Processing at the NCHS facility

in Research Triangle Park, North

Carolina. Beginning with the 1998

NHDS survey year these activities are

being done by a contractor. Sample

Listing Sheets and abstracts received by

NCHS are recorded and tracked through

a receipt and control process to monitor

data flow and completeness. During this

process, batches consisting of

approximately 1,000 abstracts are

formed and identified to track and

conduct medical coding, data entry, and

quality control

Trained medical coding personnel

code diagnoses and procedures using the

ICD–9–CM. A minimum of one and a

maximum of seven diagnostic codes are

assigned for each sample abstract. If an

abstract included surgical and/or

diagnostic procedures, a maximum of

four codes are assigned.

Beginning in 1986 annual

modifications or addenda have been

made to the ICD–9–CM. These

addenda, which go into effect on

October 1 of each year, added, deleted,

or modified existing codes. However,

because the NHDS is conducted for

calendar years, the addenda are not

incorporated into the manual coding

process until the next survey year

(beginning January 1, 3 months after the

effective date). This results in consistent

coding for all medical data for the

calendar survey year.

There is quality control for medical

coding and data entry. This procedure is

based on a 5-percent sample for each

batch (group of 1,000 abstracts) in

which abstracts are independently coded

by a second coder, with discrepancies

adjudicated by a chief coder. Batches for

which the quality control sample have

an error rate greater than 5 percent for

medical data or 1 percent for

nonmedical data are rejected and

recoded. The overall error rate for

records manually coded for the 1997

data year was 1.0 percent for final

diagnoses, 0.7 for surgical and

diagnostic procedures, and 0.2 percent

for nonmedical data entry.

Automated Data Collection

and Processing

Of the factors that influenced the

redesign of the NHDS, the use of

discharge data in computerized form

has had the greatest impact on the

ongoing operations of the survey.

Because hospital participation is

voluntary, NCHS cannot require

hospitals or their intermediaries who

supplied discharge data in machine

readable form to comply with standard

file and variable formats. And, with

limited survey resources, NCHS cannot

afford to have automated data sent to

NCHS in a defined format. As a result,

in many instances unique procedures for

processing electronic files were

developed, and these procedures have

been subject to regular change as the

sources of data changed. What became

known as ‘‘automated’’ data collection

in NHDS has been a dynamic process.

This section provides background to and

a general description of NHDS

automated data collection and its

processing.

Background

The concept of collecting data on

health encounters through existing

electronic systems was formalized in the

1970’s as part of the NCHS’s

Cooperative Health Statistics System

(CHSS). The CHSS operated under the

legislative authority of the Health

Services Research, Health Statistics, and

Medical Libraries Act of 1974 (Public

Law 93–353) (15). A major emphasis of

the CHSS was national data collection

through a ‘‘bottom-up’’ cooperative

arrangement, a system in which data

would be collected once, processed

initially at the State level, and submitted

to the Federal level in machine readable

form to provide national data. During

the 1970’s, under the CHSS, NCHS

funded hospital discharge demonstration

projects in 12 States. This activity ended

at NCHS in February 1979, by a

decision of the Secretary of Health,

Education, and Welfare (16).

A general evaluation study of the

NHDS conducted in the mid-1970’s (17)

recommended that the NHDS collect

data from three frames: 1) hospitals

covered by the CHSS, 2) non-CHSS

hospitals that were members of a private

abstracting system, and 3) all other

hospitals for which no special data

source was available. In order to

implement a plan that incorporated

automated data collection, two major

issues needed to be addressed: the

availability and quality of data from

these sources. The evaluation study

concluded that all the NHDS data items,

with the exception of marital status,

were widely available from automated

sources.

Studies conducted in the late 1970’s

on the reliability of hospital discharge

abstract service data (18) and on the

reliability of the NHDS data (19)

showed that data collected from

hospitals for discharges by abstract

services met and in some cases

exceeded standards of data quality

traditionally held by NCHS. More

recently there has been evidence of

improvement in the general quality of

hospital discharge data files as this

information became important for

determining reimbursement by Medicare

and other payers (20–22).

NCHS funded two studies on the

operational aspects of collecting data in

electronic form from abstract services.

The first study, initiated in 1980 (23),

focused on the suitability of purchasing

and using data from discharge abstract

services in the NHDS. One of the

findings from this study was that the

purchase of data could greatly reduce,

but not eliminate, the need for direct

data collection. In 1981 approximately

60 percent of hospitals in the United

States subscribed to discharge abstract

service systems that serviced 10 or more

hospitals. Without covering the universe

of hospitals, these systems could not

provide a representative sample of all

hospitals in the United States.

Page 6 [ Series 1, No. 39
Under the second study, NCHS

initiated a demonstration project in 1984

(24) to develop procedures for

acquiring, processing, and validating the

quality of existing discharge data in

electronic form. Under this contract

automated data were collected from

commercial abstract services for 76

hospitals that participated in the NHDS.

Estimates from NHDS based on data

collected by both means (manual and

automated) produced comparable results

(25). The study also demonstrated that

abstracting service organizations could

comply with data delivery schedules

necessary for NHDS. Based on the

results of this study, NCHS began to use

data in automated form in the 1985

NHDS.

For the 3 years, 1985–87, NCHS

acquired existing automated inpatient

data for some NHDS hospitals under a

contract with the Center for Health

Policy Studies (CHPS). CHPS provided

NCHS with a census file for all

discharges for 78, 77 and 74 hospitals,

respectively, for each of these years and

NCHS sampled records from these files

based on the sample design for manual

data collection.

Beginning in 1988 purchasing and

processing of data in automated form

was conducted by NCHS. Automated

data collection increased to include

about 170 hospitals annually (table B)

and the design specifications provided

for a greater number of sample

discharges from hospitals that provided

data in machine readable form.

Data Sources

In 1987 NCHS requested client lists

from 22 major hospital discharge

abstracting services. These lists were

used to identify the abstract service for

hospitals sampled in the NHDS. Of the

542 hospitals sampled for the 1988

NHDS, 240 or 44.4 percent, used at

least one of these services.

Changes in computer technology

and the transition of automated data

from commercial services to State-based

systems resulted in a dynamic and

evolving system for processing

automated data. The mix of these

sources changed dramatically from 1988

to 1997: by 1997, most of the 22

commercial abstract processing

organizations used for the 1988 NHDS

had either closed or transformed to a

State-based system (hospital

associations, State departments of health

and State contractors). State-based

systems accounted for approximately

95 percent of all machine readable data

used in the 1997 NHDS. In 1997 the

NHDS collected automated data from 20

different automated data systems and 12

individual hospitals directly. Of the 20

systems, 16 were State systems, 2 were

corporate owned, and 2 were

commercial abstract companies.

With some exceptions, automated

data sources other than individual

hospitals (abstract services, hospital

associations, and State organizations)

were bound by contracts with their

client hospitals or by State laws to

obtain permission from hospitals before

they could release data to NCHS. This

required NCHS to go through a two-step

process in order to obtain data from

these sources. First, NCHS had to

secure permission from each hospital to

allow the automated data source to

release the hospital’s data to NCHS.

Second, NCHS had to negotiate and

establish a formal relationship with each

automated data source about issues

related to purchasing data files. For

purchasing data from individual

hospitals, elements of the process were

similar, but the process was conducted

with a single entity—the hospital.

Data Release Agreements—

Hospitals

To obtain data release agreements

from hospitals, NCHS sends an

introductory letter and packet of

information to each hospital to solicit

their participation in the survey. The

packet contains a release agreement

(appendix VIII), information about the

NCHS and NHDS, an endorsement

letter from the American Hospital

Association (appendix III), selected

endorsements from State hospital

associations, and recent publications

from the National Center for Health

Statistics using data from the NHDS.

An initial telephone call by the

NCHS staff is made to explain the

release request and obtain the name of

the hospital administrator. If the release

form is not returned within 2 weeks, the

hospital receives a follow-up telephone

call. The Census Bureau is advised of

all hospitals that were late or refused the

request, and they performed a final

follow up with the hospital to obtain a

release form. At this stage a meeting

with the hospital administrator is usually

required to obtain the hospital’s

cooperation. For individual hospitals

that supply automated data directly to

NCHS, this is the only agreement that is

needed. For hospitals that agree to have

a third party release their data to NCHS,

a copy of the release agreement between

NCHS and the hospital are forwarded to

the organization that maintains the

hospital’s discharge data.

Data Release Agreements—

Automated Discharge Data

Sources

NCHS established standard

guidelines and formal agreements

(appendix IX) for purchasing hospital

discharge data from medical record

abstract service organizations. These

agreements delineated unit record costs,

startup programming costs, delivery

schedules, tape formatting instructions,

record layouts, field and data element

definitions, and assurances of

confidentiality. Confidentiality issues in

these agreements work to each party’s

benefit: to ensure hospitals that NCHS

would not release identifying

information, and to protect NCHS from

the automated data sources divulging the

identity of hospitals that participated in

the NHDS. Whenever possible releases

were negotiated for multiple years or

were open ended to reduce the

administrative resources needed to

renegotiate annually.

Beginning in 1993 NCHS

incorporated nonconfidential data files

from State discharge data sources.

Hospital release agreements were not

required from these sources because the

data were not confidential and the data

were for research and statistical use. For

these files NCHS receives some

variables in a modified form to ensure

confidentiality. For example, exact

admission and discharge dates are

replaced with length of stay, and exact

Series 1, No. 39 [ Page 7
birth date is replaced with the patient’s

age. Data were obtained for 110

hospitals from nonconfidential sources

for the 1997 NHDS.

File Processing

Automated files of discharges and

accompanying documentation are sent

directly to NCHS. Individual hospitals

also provide statistical information about

the volume of discharges per month on

a transmittal notice (appendix X) that is

used in the estimation process.

NCHS developed a recommended

file layout with variable structures

(appendix XI) and processing

procedures for submission of automated

data. However, as a voluntary survey,

NCHS does not have authority to

require the submission of data, its

structure, or the form of its submission.

To keep the hospital response rate as

high as possible, NCHS is flexible in its

receipt of automated data. As a result,

electronic files are sent to NCHS on

various media (cartridge tapes, reel

tapes, CD-ROM, diskettes, and as

E-mail attachments); in ASCII or

EBCDIC; in various layouts and

blocking factors; for varying time

frames (quarterly, semiannually, and

annually); and often with unique

variable structures. In addition,

automated data files are accepted as a

census or sample of discharges. Census

files contain all discharges from

hospitals and sampling is performed by

NCHS (see Statistical Design). Sample

files consist of discharges that sampled

by the automated source prior to

submission to NCHS based on sampling

specifications provided by NCHS (see

Statistical Design). In all, NCHS

receives approximately 2,000,000

discharges in automated form each year

from about 35 different sources on

approximately 60 physical files.

The variety of file formats and data

structures precludes a uniform system

for processing. NCHS developed and

regularly modifies a process to

restructure variables to common

definitions, reformat files to a common

layout, and to evaluate the quality of all

automated data. Evolution of the file

processing system resulted in many

adjustments to individual data files

depending on the problems encountered.

Some activities or functions were used

once for a single file while others have

been used across years. The general

characteristics of this process are

described below. The goal was to

produce files containing data of

acceptable quality in a single format

with identical variable definitions.

Each automated file is copied to a

mainframe computer and compared with

the previous year submission from that

data source for changes in internal and

external characteristics. If a file fails to

copy correctly, further investigation is

conducted using a program to display

the encoding structure, density, internal

labeling, blocking, and record length of

the file, and also to detect the existence

of extraneous data. If a file is physically

unusable, NCHS requested a

replacement and the process began

anew.

After a file is determined to be

physically usable, a specific program is

used for each file that is not in the

recommended NCHS format to reformat

all data elements to a uniform format

with uniform data structures. At this

point automated files are examined to

detect and remove duplicate records

within hospitals.

Next, all ICD–9–CM codes on the

file are subjected to an annually updated

program that converts the ICD–9–CM

addenda effective on October 1 of the

survey year back to valid codes before

October 1 of the survey year. This

process was required to make fiscal year

ICD–9–CM codes compatible with

calendar year codes for the NHDS.

Also, there were instances in which

hospitals had not properly instituted the

addenda from previous years and

submitted files that contained codes that

were no longer in use. A computer

program was developed that changed all

outdated codes from previous years to

valid current-year codes. The first

process, changing the addenda to NHDS

survey year codes, affected thousands of

codes annually because it covered codes

from all automated discharges for the

last quarter of the survey year; the

second process involved very few codes

and none in some years.

All records are checked for invalid

or missing variables, inaccuracies,

outliers, and a detailed review is

conducted for most variables for each

hospital. For diagnoses and procedures

codes, the review process generated a

list of invalid ICD–9–CM codes,

first-listed and all-listed diagnoses, the

25 most frequently occurring diagnoses

and procedures by age group, and the

distribution of discharges for all patients

by chapters of the ICD–9–CM. For all

other variables the review involves a

comparison of distributions for the

current year with data from previous

years. This review detected potential

problems. If the problems cannot be

fixed at NCHS, a corrected file is

requested.

The final product of these

processing operations are files in a

standard format with identical variable

structures, valid survey-year ICD–9–CM

codes, and data of acceptable quality.

Using these files, data from hospitals

that provided a census of discharges are

merged to form a single file for

sampling (see Statistical Design).

To avoid disruption of the flow of

automated data for the NHDS, NCHS

needs timely information about hospitals

that changed or discontinued their

abstract service. Early knowledge of

these changes provides time to obtain

the necessary data release agreements

with these hospitals and their new

abstract service in time to process the

data. To learn about these changes,

NCHS initiated semiannual contacts

with each automated hospital as

recommended (24). In its initial form

this process was envisioned to be

conducted by sending postcards to

hospitals. The hospitals would complete

the questions and mail the

self-addressed, stamped postcard to

NCHS. However, using actual postcards

could not be accomplished

administratively, so letters are used

(appendix XII).

This activity has evolved to provide

a measure of the completeness of data

being collected for each automated

hospital. In 1997 it was conducted

semiannually to get information directly

from automated hospitals to validate

their total number of discharges,

numbers of newborns, and total hospital

beds.

Page 8 [ Series 1, No. 39
Editing

Extensive computerized edits are

applied to each record. The computer

edits are augmented by a manual review

of selected records rejected by the edit

program. The edits include validity and

range checks for nonmedical variables,

and consistency checks for dates of

admission, discharge and birth. The

medical data (diagnoses and procedures)

are verified against a list of all valid

ICD–9–CM codes. Invalid ICD–9–CM

codes are removed. The edit performs a

series of consistency tests from decision

logic tables for sex-specific and

age-specific ICD–9–CM codes. When

the sex or age of a patient is

incompatible with the recorded medical

information, priority is given to the

medical information.

With two exceptions, the order of

diagnoses and procedures for sampled

discharges is preserved to reflect the

order on the medical record face sheet

or in the automated file. One exception

is for women admitted for delivery for

whom a code of V27 from the

supplemental classification is assigned

as the first-listed code in order to

provide an estimate of all deliveries. In

the other exception, whenever an acute

myocardial infarction is present with

another circulatory diagnosis and is

other than the first-listed diagnosis, it is

reordered to the first position.

The computerized edit process

identifies some records for manual

review: records with ICD–9–CM codes

that are not valid as first-listed or

single-listed codes; all records with

lengths of stay longer than 100 days;

records that indicate a delivery with a

length of stay over 30 days; and all

records with age equal to or greater than

100 years. A nosologist at NCHS

examines these records and makes

changes as appropriate to eliminate

gross inconsistencies. In 1997, 276

records were identified for manual

review.

Imputation

Before 1996 missing values of age

and sex were imputed by using random

assignment with female being assigned

first for sex and a decision-logic table

was used to impute age. Beginning with

the 1996 NHDS a hot deck method for

missing values of age and sex has been

used that maintains the known age or

sex distribution of records within the

same 3-digit level of first-listed

ICD–9–CM diagnostic code.

Estimation Procedures

Statistics from the NHDS are

derived by a multistage estimation

procedure that produces

essentially unbiased national estimates

and has three basic components:

inflation by reciprocals of the

probabilities of sample selection,

adjustment for nonresponse, and

population weighting ratio adjustments.

The second and third components are

made separately by admission

types—that is, for discharges of

newborn infants (whose hospital stay

began with their own birth) and for

discharges other than newborn infants.

Inflation by Reciprocals of

Probabilities of Selection

The first two probabilities of the

three-stage sample design for the NHDS

are known and fixed (see Statistical

Design). However, the number of

discharges for individual months is not

always constant or an integral multiple

of the sampling fraction. For these

reasons, in the estimation process, this

probability is the ratio of the actual

number of discharges per month to the

number of sampled discharges for the

month.

Adjustment for

Nonresponse

NHDS estimates are adjusted to

account for nonresponse at two levels:

hospitals and discharges within

hospitals. Within hospital adjustments

are made for nonresponding months and

within months for nonresponding

discharges.

Hospital nonresponse occurs when

an in-scope (NHDS-eligible) sample

hospital does not respond for at least

one-half of the months during which it

was in scope. In this case, the weights

of discharges from hospitals similar to

the nonrespondent hospitals are inflated

to account for discharges represented by

the nonrespondent hospitals. For this

purpose, hospitals are judged to be

similar if they are in the same region,

hospital specialty-size group, and if

possible, the same sampling stratum

(that is, the same abstracting status

group if the nonrespondent hospital was

in the 12 largest PSU’s and in the same

PSU, otherwise).

The adjustments for this

nonresponse are made separately for

admission types— that is, for discharges

of newborn infants and for all other

discharges. The adjustment consists of a

ratio for which the numerator is the

weighted number of discharges of the

admission type in all similar sample

hospitals (regardless of response status)

and the denominator is the weighted

total of discharges of that admission

type from the respondent hospitals

similar to the nonrespondent hospitals.

Data on the number of discharges for

each admission type for each hospital

come from either the hospitals or the

April SMG Hospital Market Database

for the survey year.

At the discharge level, responding

hospitals have a month(s) of

nonresponse when the number of

discharges received for the month was

less than one-half of the expected

number of discharges. For a hospital’s

month(s) of nonresponse, the weights of

discharges in the hospital’s respondent

months are inflated by ratios that varied

with discharge groups defined by the

ICD–9–CM diagnostic classes of those

discharges’ first-listed diagnoses. The

adjustment ratio for each partially

respondent hospital and each discharge

group is calculated using only data from

sample hospitals that were NHDS

eligible and respondent for all 12

months of the data year. The ratio has as

its numerator the weighted sum of

discharges in that discharge group for all

months in which the partially respondent

hospital was in scope. The ratio has as

its denominator the weighted sum of

discharges in that discharge group that

occurred in the months when the

Series 1, No. 39 [ Page 9
partially respondent hospital did respond

to the NHDS.

Discharge nonresponse also occurs

when NCHS fails to collect all of the

discharge abstracts expected for a month

(the number expected was the product

of the hospital’s total discharges each

month and the discharge sampling rate

assigned to the hospital). In each month

when the hospital was respondent (at

least one-half of the expected abstracts

were collected), the weights of abstracts

collected for the month are inflated to

account for the missing abstracts.

Population Weighting

Ratio Adjustment

The final adjustment consists of a

population weighting ratio adjustment

that is applied separately for newborns

and for other than newborns. These

adjustments are made within each of 16

noncertainty hospital groups defined by

region and hospital specialty-size classes

to adjust for oversampling or

undersampling of discharges reported in

the sampling frame for the data year.

For discharges other than newborn

infants, the adjustment is a

multiplicative factor that has as its

numerator the number of admissions

reported for the year at sampling frame

hospitals within each region-specialtysize group and as its denominator the

estimated number of those admissions

for that same hospital group. The

adjustment for discharges of newborn

infants is similar, but numbers of births

are used in place of admissions. The

ratio numerators are based on the figures

obtained annually from the SMG

Hospital Market Database and the ratio

denominators are obtained through a

simple inflation of the SMG figures for

the NHDS sample hospitals. NCHS

performs a review for outliers found by

comparing the SMG Hospital Market

Database file for the current and

previous years. The object of this review

is to allow detection of potential

systematic problems and to correct the

file prior to weighting.

Reliability of

Estimates

Because the statistics from the

survey are based on a sample,

they may be different from the

figures that would have been obtained if

a complete census had been taken using

the same forms, definitions, instructions,

and procedures. However, the

probability design of the NHDS permits

the calculation of sampling errors. The

standard error of a statistic is primarily

a measure of sampling variability that

occurs by chance because only a sample

rather than the entire population is

surveyed. The standard error, as

calculated for the NHDS, also reflects

part of the variation that arises in the

measurement process, but does not

include any systematic bias that may be

in the data. The relative standard error

(RSE) of an estimate is obtained by

dividing the standard error by the

estimate itself and when multiplied by

100 is expressed as a percent of the

estimate. Generally, in tables of NCHS

published data reports, an asterisk (*) is

used to indicate the relative unreliability

of estimates based on fewer than 30

records or records that have a relative

standard error greater than 30 percent.

In repeated samples using the same

forms and procedures, the chances are

about 68 in 100 that an estimate from

the sample would differ from a complete

census by less than the standard error.

The chances are about 95 in 100 that

the difference would be less than twice

the standard error, and about 99 in 100

that it would be less than 2.5 times as

large.

Estimation of Standard

Errors

Beginning with the 1988 NHDS,

estimates of sampling variability for the

NHDS statistics presented in NCHS

publications have been computed using

software that produces error estimates

for statistics from complex sample

surveys. The software employs a

first-order Taylor Series approximation

of the deviation of estimates from their

expected values. A description of this

software and the approach it uses has

been published (6,7).

Standard Error

Approximations

Parameters for calculating

approximate relative standard errors for

aggregate estimates are presented in

table C. To derive error estimates that

would be applicable to a wide variety of

statistics, numerous estimates and their

variances are produced. A least-squares

method is then used to produce best-fit

curves, based on the empirically

determined relationship between the size

of an estimate X and its relative

variance. The relative standard error of

an estimate X [RSE(X)] is the square

root of the relative variance and may be

calculated from the formula:

RSE(X) = √a + b/X

with a and b provided in table C. When

multiplied by 100, the RSE(X) is

expressed as a percent of X.

For example, in 1997 the estimated

number of discharges from short-stay

hospitals for females with a first-listed

diagnosis of atherosclerotic heart disease

(ICD–9–CM code 414.0) was 384,000.

Using the applicable constants from

table C for estimates by sex produces:

RSE384,000=

√.00127 + (325.984/384,000)

RSE(384,000) = .046

When multiplied by 100, the

relative standard error for the estimate

of interest becomes 4.6 percent. The

standard error of the estimate is

obtained by multiplying the relative

standard error by the estimate itself:

SE(384,000) = 384,000 * .046 = 17,664

The standard error can be employed

to generate confidence intervals for

statistical testing. In this example, the

95 percent confidence interval for the

Page 10 [ Series 1, No. 39
estimate of female inpatients with a

first-listed diagnosis of atherosclerotic

heart disease is:

(384,000 – 2 *17,664) <->

(384,000 + 2 * 17,664)

348,700 <-> 419,300

Relative Standard Error

for Estimates of Percents

Approximate relative standard errors

for estimates of percents may be

calculated from table C also. The

relative standard error for a percent,

100 p (0 < p< 1) may be calculated using

the formula:

RSEp) = √ b * (1–p)/(p * X)

where 100p is the percent of interest, X

is the base of the percent, and b is the

parameter b in the formula for

approximating the RSE(X). The values

for b are given in table C. When

multiplied by 100, the RSE(p) is

expressed as a percent of the

estimate, p.

For example, in 1997 the estimated

number of discharges from short-stay

hospitals that were female was

18,647,000. This is 60.3 percent of the

estimated 30,914,000 discharges for that

year. Using the applicable constants

from table C for estimates by sex

produces:

RSE.603=

√325.984 * (1 – .603) / (.603 * 30914000)

RSE(.603) = .002635

When multiplied by 100, the

relative standard error for the estimate

of interest becomes .2635 percent. From

this the standard error is obtained by

multiplying the relative standard error

by the estimate itself:

SE(.603) = .603 * 0.002635 = .0016

The standard error can be employed to

generate confidence intervals for

statistical testing. In this example, the

95 percent confidence interval for the

estimate of the percent of female

inpatients is:

(.603 – 2 * .0016) <-> (.603 + 2 * .0016)

.5998 <-> .6062

or, equivalently, 59.98 percent <->

60.62 percent

The SUDAAN software can be used

to compute specific standard errors for

the NHDS estimates from which relative

standard errors may be derived. The

files needed to use SUDAAN have not

been publicly released because they

contain information that is confidential

(however, recently these files have

become available for analysis, see Data

Table C. Estimated parameters for approximate relative standard error equations, by selected characteristics: National Hospital Discharge

Survey, 1997

First-listed diagnosis Days of care All-listed diagnosis All-listed procedures

a b a b ab a b

Total ..................... 0.00132 313.983 0.00242 1,036.029 0.00271 428.987 0.00288 323.247

Sex

Male ..................... 0.00148 335.128 0.00299 1,309.507 0.00214 307.917 0.00268 380.213

Female ................... 0.00127 325.984 0.00252 1,060.275 0.00127 311.394 0.00197 299.725

Age group

Under 15 years .............. 0.01470 181.262 0.02393 346.675 0.01617 223.921 0.02639 196.719

15–44 years ................ 0.00137 294.357 0.00285 934.043 0.00151 309.115 0.00219 305.574

45–64 years ................ 0.00138 301.320 0.00284 1,248.476 0.00290 370.245 0.00235 298.267

65 years and over............. 0.00147 343.779 0.00275 1,866.761 0.00144 361.717 0.00239 292.252

Region

Northeast .................. 0.00384 195.564 0.00863 495.447 0.00592 239.709 0.00695 219.126

Midwest ................... 0.00609 191.492 0.00866 481.071 0.00853 180.424 0.00870 163.190

South .................... 0.00369 320.084 0.00572 1,581.301 0.00307 341.005 0.00498 274.548

West . . . . . . . . . . . . . . . . . . . . . 0.00513 338.516 0.01008 926.285 0.00508 378.827 0.00663 288.835

Race

White..................... 0.00300 314.704 0.00480 1,103.096 0.00357 314.530 0.00463 369.830

Black ..................... 0.00529 248.048 0.00822 875.877 0.00519 236.801 0.00662 225.180

All other ................... 0.01770 200.033 0.02524 581.314 0.01615 224.604 0.02070 211.065

Race not stated .............. 0.01973 196.517 0.02387 394.423 0.02002 187.166 0.02126 142.769

Expected source of payment

Worker’s compensation ......... 0.00721 320.711 0.01413 896.903 0.01093 337.073 0.01143 270.432

Medicare .................. 0.00171 325.698 0.00301 1,822.158 0.00157 372.529 0.00264 297.577

Medicaid................... 0.00438 293.366 0.00709 685.261 0.00379 287.541 0.00540 282.342

Payment not stated ............ 0.00962 313.407 0.01966 1,484.182 0.01219 310.942 0.01814 248.591

Other government payments ...... 0.00181 278.864 0.00345 617.794 0.00199 299.815 0.00265 289.092

Private insurance ............. 0.00373 265.383 0.00994 854.606 0.00415 281.681 0.00689 227.293

Self-pay ................... 0.02771 94.095 0.03240 244.803 0.03212 127.947 0.03297 94.813

No charge/other .............. 0.01828 394.867 0.02548 1,488.967 0.01931 386.315 0.02059 388.354

Series 1, No. 39 [ Page 11
Dissemination). The generalized

procedure for approximating relative

standard errors for the NHDS described

above is widely applicable for a variety

of statistics and cost efficient. As a

result, standard errors computed from

the generalized curves should be

interpreted as approximate rather than

exact for any specific estimate.

Nonsampling Errors

Estimates from the NHDS are

subject to nonsampling as well as

sampling errors, as are estimates from

any survey. For the NHDS nonsampling

errors may include those due to

sampling frame errors, hospital

nonresponse, missing abstracts, and

errors introduced at the time of data

collection or electronic data entry.

Although the magnitude of the

nonsampling errors cannot be computed,

these errors were kept to a minimum by

procedures built into the operation of

the survey.

Errors resulting from the exclusion

of in-scope hospitals from the sampling

frame are believed to be small because

the hospitals excluded were hospitals

that opened after the frame was

constructed and, hence, they tend to

have few discharges relative to hospitals

that were in the frame. Other

nonsampling errors were kept to a

minimum by training the data collectors

in sampling and data abstraction, quality

control procedures, and edit checks

discussed in the data processing section.

Because the survey results are subject to

sampling and nonsampling errors, the

total error is larger than the error

due to sampling variability alone.

Data Dissemination

Data are available for all years of

the survey, but the mechanisms

for data release have changed to

reflect the needs of data users and new

technology. This section summarizes the

current methods of data release for the

NHDS.

Summary data from NHDS have

been published annually for three levels

of statistical detail: the Advance Data

From Vital and Health Statistics (26)

utilizes a brief format for reporting of

inpatient statistics as soon as possible

after the survey has been completed;

more detailed summary statistics are

available from Series 13 Vital and

Health Statistics (27); and discharge

estimates for individual ICD–9–CM

diagnostic and procedure codes have

been published in Series 13, Vital and

Health Statistics (28). Series 13 Vital

and Health Statistics reports that

combined ambulatory surgery and

surgery performed on hospital inpatients

for 1994, 1995, and 1996 are available

(29–31). In addition, there are reports

comparing hospital use in the United

States and other countries under Series

5, Comparative International Vital and

Health Statistics Reports; trend reports

under Series 13, Vital and Health

Statistics; and, methodological reports

using hospital survey data published in

Series 2, Vital and Health Statistics

(32). Reports on topics of special

interest have been published in Advance

Data From Vital and Health Statistics,

Series 13 Vital and Health Statistics

reports, and in published journal articles

and papers presented at professional

meetings (33–34). As resources permit,

special tabulations and analyses are

provided to data requestors inside and

outside the Federal Government.

For each survey year, a public-use

data tape and documentation are

prepared for distribution through the

National Technical Information Service

(NTIS). NCHS has also produced a

multiyear data file (1979–97), which is

available on data tape and CD-ROM.

For analysts interested in going beyond

what is available in the public use files,

NCHS has established a Research Data

Center that allows the use of SUDAAN

and linking NHDS data with other

sources of information.

A Catalog of Publications and a

Catalog of Public-Use Data Tapes from

the National Center for Health Statistics

are available via the Internet (at:

www.cdc.gov/nchswww/products/

products.htm) or from NCHS (Data

Dissemination Branch, National Center

for Health Statistics, 6525 Belcrest

Road, Room 1064, Hyattsville,

Maryland 20782; Telephone (301)

436–8500). Many of the publications,

data files and file documentation

mentioned above are available at this

Internet site.

References

1. Origin, Program, and Operation of the

U.S. National Health Survey. National

Center for Health Statistics. Vital

Health Stat 1(1). 1965.

2. Woolsey TD. ‘‘Hospital Statistics from

the U.S. National Health Survey.’’

Presentation for Annual Conference for

Executives of Allied Hospital

Association, Grand Hotel, Mackinac

Island, Michigan. July 1963.

3. U. S. Bureau of the Census. Statistical

abstract of the United States: 1997.

117th ed. Washington: 1997.

4. Simmons WR. Development of the

design of the NCHS Hospital Discharge

Survey. National Center for Health

Statistics. Vital Health Stat 2 (39).

1970.

5. Massey JT, Moore TF, Parsons VL,

Tadros W. Design and estimation for

the National Health Interview Survey,

1985–94. National Center for Health

Statistics. Vital Health Stat 2(110).

1989.

6. Shah BV. SESUDAAN: Standard errors

program for computing of standardized

rates from sample survey data.

Research Triangle Park, North Carolina.

Research Triangle Institute. 1981.

7. Shah BV, Barnwell BG, Hunt PN,

LaVange LM. SUDAAN user’s manual,

release 5.50. Research Triangle Park,

North Carolina: Research Triangle

Institute. 1991.

8. Haupt BJ, Kozak LJ. Estimates from

two survey designs: National Hospital

Discharge Survey. National Center for

Health Statistics. Vital Health Stat

13(111). 1992.

9. Shimizu I, Cole C. A comparison of

precision between two- and three-stage

designs for National Hospital Discharge

Survey. Proc Amer Statist Ass. Survey

Research Methods Section. 1991.

10. SMG Hospital Marketing Group, Inc.

Hospital market database. Healthcare

Information Specialists. Chicago,

Illinois: 1987.

11. Moien M. The use of hospital discharge

survey data to produce trend estimates

of hospital utilization. Proc Amer

Statist Ass. Social Statistics Section.

1978.

12. National Center for Health Statistics.

International Classification of Diseases,

Page 12 [ Series 1, No. 39
9th Revision, clinical modification.

Washington: Public Health Service.

1980.

13. Report of the U.S. Committee on Vital

and Health Statistics. Uniform hospital

abstract: minimum basic data set.

National Center for Health Statistics.

Vital Health Stat. 4 (14). 1975.

14. Department of Health and Human

Services. Health information policy

council: 1984 revision of the uniform

hospital discharge data set. Office of

the Secretary. Federal Register; vol 50

no 147. 1985.

15. Task Force on Definitions. The

cooperative health statistics system: Its

mission and program. National Center

for Health Statistics. Vital Health Stat.

4 (19). 1977.

16. Final of the Panel to Evaluate the

Cooperative Health Statistics System.

Directions for the 80’s. National Center

for Health Statistics. Hyattsville,

Maryland: 1980.

17. Lissler JT. Hospital discharge survey

evaluation study. Contract NCHS

255U-1178. Research Triangle Park,

North Carolina: Research Triangle

Institute. 1977.

18. Institute of Medicine. Reliability of

hospital discharge abstracts.

Washington: National Academy of

Sciences. 1977.

19. Institute of Medicine. Reliability of

National Hospital Discharge Survey

data. Washington: National Academy of

Sciences. 1980.

20. Green J, Wintfeld N. How accurate are

hospital discharge data for evaluating

effectiveness of care? Med care

31:719–31. 1993.

21. Fisher ES, Whaley FS, Krushat, et al.

Accuracy of Medicare’s hospital claims

data: Progress has been made, but

problems remain. Am J Public Health

82:243–8. 1992.

22. Hsia DC, Ahern CA, Ritchie, et al.

Medicare reimbursement accuracy

under the prospective payment system,

1985 to 1988. JAMA 268:896. 1992.

23. Duggar BC, et al. Alternative sources

for producing national statistics on

hospital utilization. Contract NCHS

223–81-2057. JRB Associates. 1981.

24. Miller H, et al. Optional methods for

collecting data for the National

Hospital Discharge Survey. Contract

NCHS 282–84-2107. Center for Health

Policy Studies. 1984.

25. Tompkins L. Comparison of manually

abstracted and automated abstract

service data in the 1984 NHDS.

Unpublished paper prepared by the

Office Research and Methodology for

review within NCHS. 1989.

26. Graves GJ, Owings MF. 1996

Summary: National Hospital Discharge

Survey. Advance data from vital and

health statistics; no 301. Hyattsville,

Maryland: National Center for Health

Statistics. 1998.

27. Graves GJ, Kozak LJ. National

Hospital Discharge Survey: Annual

summary, 1996. National Center for

Health Statistics. Vital Health Stat

13(140). 1999.

28. Graves GJ, Kozak LJ. Detailed

diagnoses and procedures, National

Hospital Discharge Survey 1996.

National Center for Health Statistics.

Vital Health Stat 13(138). 1997.

29. Pokras R, Kozak LJ, McCarthy E.

Ambulatory and inpatient procedures in

the United States, 1994. National

Center for Health Statistics. Vital

Health Stat 13(132). 1997.

30. Kozak LJ, Owings MF. Ambulatory

and inpatient procedures in the United

States, 1995. National Center for

Health Statistics. Vital Health Stat

13(135). 1998.

31. Kozak LJ, Owings MF. Ambulatory

and inpatient procedures in the United

States, 1996. National Center for

Health Statistics. Vital Health Stat

13(139). 1998.

32. Harris KW, Hoffman KL. Quality

control in the Hospital Discharge

Survey. National Center for Health

Statistics. Vital Health Stat 2(68). 1975.

33. Pappas G, Hadden WC, Kozak LJ,

Fisher GF. Potentially avoidable

hospitalizations: Inequalities in rates

between U.S. socioeconomic groups.

Am J Public Health 87(5):811–6. 1997.

34. Wilcox SW, Koonin LM, Pokras R, et

al. Hysterectomy in the United States,

1988–1990. Obstet Gynecol

83(4):549–55. 1994.

Series 1, No. 39 [ Page 13
Appendix I.

Legislative Authorization

Public Health Service Act

Section 306(a) & (b)

NATIONAL CENTER FOR HEALTH STATISTICS

Section 306. [242k](a) There is established in the Department of Health and Human Services the National Center for Health

Statistics (hereinafter in this section referred to as the ‘‘Center’’) which shall be under the direction of a Director who shall be

appointed by the Secretary and supervised by the Assistant Secretary for Health (or such officer of the Department as may be

designated by the Secretary as the principal adviser to him for health programs).

(b) In carrying out section 304(a), the Secretary, acting through the Center-

(1) shall collect statistics on-

(A) the extent and nature of illness and disability of the population of the United States (or any groupings of people

included in the population), including life expectancy, the incidence of various acute and chronic illnesses, and infant and

maternal morbidity and mortality,

(B) the impact of illness and disability of the population on the economy of the United States and on other aspects of the

well-being of its population (or of such groupings),

(C) environmental, social, and other health hazards,

(D) determinants of health,

(E) health resources, including physicians, dentists, nurses, and other health professionals by specialty and type of practice

and supply of services by hospitals, extended care facilities, home health agencies, and other health institutions,

(F) utilization of health care, including utilization of (i) ambulatory health services by specialties and type of practice of

health professionals providing such service, and (ii) services of hospitals, extended care facilities, home health agencies,

and other institutions,

(G) health care costs and financing, including the trends in health care prices and costs, the sources of payments for

health care services, and Federal, State, and local governmental expenditures for health care services, and

(H) family formation, growth, and dissolution;

(2) shall undertake and support (by grant or contract) research, demonstrations, and evaluations respecting new or

improved methods for obtaining current data on the matters referred to in a paragraph (1);

(3) may undertake and support (by grant or contract) epidemiologic research, demonstrations, and evaluations on the

matters referred to in paragraph (1); and ....‘‘

(4) may collect, furnish, tabulate, and analyze statistics, and prepare studies, on matters referred to in paragraph (1) upon

request of public and nonprofit entities under arrangements under which the entities will pay the cost of the service provided.

Amounts appropriated to the Secretary from payments made under arrangements made under paragraph (4) shall be available

to the Secretary for obligation until expended.

Page 14 [ Series 1, No. 39
Appendix II

Induction Letter

Series 1, No. 39[ Page 15
Appendix III

American Hospital Association

Endorsement Letter

Page 16 [ Series 1, No. 39
Appendix IV

Confidentiality Letter

Series 1, No. 39[ Page 17
Appendix V

Hospital Interview Questionnaire (HDS-11)

Page 18 [ Series 1, No. 39
Series 1, No. 39 [ Page 19
Page 20 [ Series 1, No. 39
Series 1, No. 39 [ Page 21
Page 22 [ Series 1, No. 39
Series 1, No. 39 [ Page 23
Page 24 [ Series 1, No. 39
Series 1, No. 39 [ Page 25
Page 26 [ Series 1, No. 39
Series 1, No. 39 [ Page 27
Page 28 [ Series 1, No. 39
Appendix VI

Medical Abstract—National Hospital Discharge Survey

Series 1, No. 39 [ Page 29
Page 30 [ Series 1, No. 39
Appendix VII

Sample Selection Sheet (HDS-5)

Series 1, No. 39 [ Page 31
Appendix VIII

Statement of Agreement

Page 32 [ Series 1, No. 39
Appendix IX

Abstract Service Agreement

Series 1, No. 39 [ Page 33
Page 34 [ Series 1, No. 39
Series 1, No. 39 [ Page 35
Appendix X

Transmittal Notice

Page 36 [ Series 1, No. 39
Appendix XI

Automated File Layout

Series 1, No. 39[ Page 37
Page 38 [ Series 1, No. 39
Series 1, No. 39 [ Page 39
Page 40 [ Series 1, No. 39
Appendix XII

Information Request Letter

Series 1, No. 39 [ Page 41
Appendix XIII

Definitions of Terms

Related to the Survey

Hospital—Hospital with an average

length of stay of less than 30 days for

all patients. Hospitals whose specialty

was general (medical or surgical) or

children’s general were included,

regardless of length of stay. Federal

hospitals, hospital units of institutions,

and hospitals with less than six beds

staffed for patients’ use are not included.

Type of ownership of hospital—

The type of organization that controls

and operates the hospital. Hospitals are

grouped as follows:

Not for profit—Hospital operated by

a church or another not-for-profit

organization.

Government—Hospital operated by

State and local government.

Proprietary—Hospital operated by

individuals, partnerships, or corporations

for profit.

Inpatient—A person who is

formally admitted to the inpatient

service of a short-stay hospital for

observation, care, diagnosis, or

treatment. The terms ‘‘inpatient’’ and

‘‘patient’’ are used synonymously.

Newborn infant—A patient admitted

by birth to a hospital.

Discharge—The formal release of a

patient by a hospital; that is, the

termination of a period of

hospitalization by death or by

disposition to place of residence, nursing

home, or another hospital. The terms

‘‘discharges’’ and ‘‘patients discharged’’

are used synonymously.

Average length of stay—The

number of days of care accumulated by

patients discharged during the year

divided by the number of these

discharges.

Diagnosis—A disease or injury (or

factor that influences health status and

contact with health services that is not

itself a current illness or injury) listed

on the medical record of a patient.

Principal diagnosis—The condition

established after study to be chiefly

responsible for occasioning the

admission of the patient to the hospital

for care.

First-listed diagnosis—The

diagnosis specified as the principal

diagnosis on the face sheet or discharge

summary of the medical record, or if the

principal diagnosis is not specified, the

diagnosis listed first on the face sheet or

discharge summary of the medical

record. The number of first-listed

diagnoses is equivalent to the number of

discharges.

Procedure—A surgical or

nonsurgical operation, diagnostic

procedure, or special treatment reported

on the medical record of a patient.

Rate of procedures—The ratio of

the number of procedures during a year

to the number of persons in the civilian

population on July 1 of that year

determines the rate of procedures.

Population—The U.S. resident

population excluding members of the

Armed Forces.

Age—Patient’s age at the birthday

before admission to the hospital.

Geographic region—Hospitals are

classified by location in one of the four

geographic regions of the United States

that correspond to those used by the

U.S. Bureau of the Census.

Region States included

Northeast Maine, New Hampshire,

Vermont, Massachusetts,

Rhode Island, Connecticut,

New York, New Jersey,

and Pennsylvania

Midwest Michigan, Ohio, Illinois,

Indiana, Wisconsin,

Minnesota, Iowa, Missouri,

North Dakota, South

Dakota, Nebraska, and

Kansas

South Delaware, Maryland,

District of Columbia,

Virginia, West Virginia,

North Carolina, South

Carolina, Georgia, Florida,

Kentucky, Tennessee,

Alabama, Mississippi,

Arkansas, Louisiana,

Oklahoma, and Texas,

West Montana, Idaho, Wyoming,

Colorado, New Mexico,

Arizona, Utah, Nevada,

Washington, Oregon,

California, Hawaii, and

Alaska

Page 42 [ Series 1, No. 39
Vital and Health Statistics

series descriptions

SERIES 1. Programs and Collection Procedures—These reports

describe the data collection programs of the National Center

for Health Statistics. They include descriptions of the methods

used to collect and process the data, definitions, and other

material necessary for understanding the data.

SERIES 2. Data Evaluation and Methods Research—These reports are

studies of new statistical methods and include analytical

techniques, objective evaluations of reliability of collected data,

and contributions to statistical theory. These studies also

include experimental tests of new survey methods and

comparisons of U.S. methodology with those of other

countries.

SERIES 3. Analytical and Epidemiological Studies—These reports

present analytical or interpretive studies based on vital and

health statistics. These reports carry the analyses further than

the expository types of reports in the other series.

SERIES 4. Documents and Committee Reports—These are final

reports of major committees concerned with vital and health

statistics and documents such as recommended model vital

registration laws and revised birth and death certificates.

SERIES 5. International Vital and Health Statistics Reports—These

reports are analytical or descriptive reports that compare U.S.

vital and health statistics with those of other countries or

present other international data of relevance to the health

statistics system of the United States.

SERIES 6. Cognition and Survey Measurement—These reports are

from the National Laboratory for Collaborative Research in

Cognition and Survey Measurement. They use methods of

cognitive science to design, evaluate, and test survey

instruments.

SERIES 10. Data From the National Health Interview Survey—These

reports contain statistics on illness; unintentional injuries;

disability; use of hospital, medical, and other health services;

and a wide range of special current health topics covering

many aspects of health behaviors, health status, and health

care utilization. They are based on data collected in a

continuing national household interview survey.

SERIES 11. Data From the National Health Examination Survey, the

National Health and Nutrition Examination Surveys, and

the Hispanic Health and Nutrition Examination Survey—

Data from direct examination, testing, and measurement on

representative samples of the civilian noninstitutionalized

population provide the basis for (1) medically defined total

prevalence of specific diseases or conditions in the United

States and the distributions of the population with respect to

physical, physiological, and psychological characteristics, and

(2) analyses of trends and relationships among various

measurements and between survey periods.

SERIES 12. Data From the Institutionalized Population Surveys—

Discontinued in 1975. Reports from these surveys are

included in Series 13.

SERIES 13. Data From the National Health Care Survey—These reports

contain statistics on health resources and the public’s use of

health care resources including ambulatory, hospital, and longterm care services based on data collected directly from

health care providers and provider records.

SERIES 14. Data on Health Resources: Manpower and Facilities—

Discontinued in 1990. Reports on the numbers, geographic

distribution, and characteristics of health resources are now

included in Series 13.

SERIES 15. Data From Special Surveys—These reports contain statistics

on health and health-related topics collected in special

surveys that are not part of the continuing data systems of the

National Center for Health Statistics.

SERIES 16. Compilations of Advance Data From Vital and Health

Statistics—Advance Data Reports provide early release of

information from the National Center for Health Statistics’

health and demographic surveys. They are compiled in the

order in which they are published. Some of these releases

may be followed by detailed reports in Series 10–13.

SERIES 20. Data on Mortality—These reports contain statistics on

mortality that are not included in regular, annual, or monthly

reports. Special analyses by cause of death, age, other

demographic variables, and geographic and trend analyses

are included.

SERIES 21. Data on Natality, Marriage, and Divorce—These reports

contain statistics on natality, marriage, and divorce that are

not included in regular, annual, or monthly reports. Special

analyses by health and demographic variables and

geographic and trend analyses are included.

SERIES 22. Data From the National Mortality and Natality Surveys—

Discontinued in 1975. Reports from these sample surveys,

based on vital records, are now published in Series 20 or 21.

SERIES 23. Data From the National Survey of Family Growth—These

reports contain statistics on factors that affect birth rates,

including contraception, infertility, cohabitation, marriage,

divorce, and remarriage; adoption; use of medical care for

family planning and infertility; and related maternal and infant

health topics. These statistics are based on national surveys

of women of childbearing age.

SERIES 24. Compilations of Data on Natality, Mortality, Marriage,

Divorce, and Induced Terminations of Pregnancy—

These include advance reports of births, deaths, marriages,

and divorces based on final data from the National Vital

Statistics System that were published as supplements to the

Monthly Vital Statistics Report (MVSR). These reports provide

highlights and summaries of detailed data subsequently

published in Vital Statistics of the United States. Other

supplements to the MVSR published here provide selected

findings based on final data from the National Vital Statistics

System and may be followed by detailed reports in Series 20

or 21.

For answers to questions about this report or for a list of reports published in

these series, contact:

Data Dissemination Branch

National Center for Health Statistics

Centers for Disease Control and Prevention

6525 Belcrest Road, Room 1064

Hyattsville, MD 20782-2003

(301) 458-4636

E-mail: nchsquery@cdc.gov

Internet: www.cdc.gov/nchs/
DHHS Publication No. (PHS) 2001-1315, Series 1, No. 390-0613 (12/00)

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