NATIONAL CENTER Series 4 

For HEALTH STATISTICS INumber 11 

VITAL amd HEALTH STATISTICS 

DOCUMENTS AND COMMITTEE REPORTS 

PROPERTYOF THE 

PUBLICATIONS8F?ANC~ 

EDITORIAL LIBMY 

use of hospital data for 

Epidemiologicand 

Medical-Care Research 

A Report of the United States National 

Committee on Vital and Health Statistics 

How hospital data may be used for epidemiologic and medicalcare research is discussed with examples of past applications. 

U.S. DEPARTMENT OF HEALTH, EDUCATION, AND WELFARE 

Public Health Service 

Health Services and Mental Health Administration 

Washington, D. Cl. June 1969 
Public Health Service Publication No. 1000-Series 4 -No. 11 

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D. C., 20402- Price 25 cents 
NATIONAL CENTER FOR HEALTH STATISTICS 

THEODORE D. WOOLSEY, Director 

PHILIP S.LAWRENCE, SC.D., Associate Director 

OSWALD K. SAGEN, PH.D.>, Assistant Director for Health Statistics Development 

WALT R. SIMMONS, M.A., Assistant Director for Research and Scientific Development 

ALICE M. WATERHOUSE, M.D.,Medical Consultant 

JAMES E. KELLY, D. D. S., Dental Advisor 

EDWARD E. MINTY, Executive O//icer 

MARGERY R. CUNNINGHAM, Information O//icer 

OFFICE OF HEALTH STATISTICS ANALYSIS 

IWAOM.MORIYAMA,Ph.D.,Di~ector 

DEAN E. KRUEGER, Deputy Directo~ 

Public Health Service Publication No. 1000-Series 4-No. 11 

Library of Congress Catalog Card Number 70-600272 
FOREWORD


This report, prepared by a Subcommittee of the U.S. National 

Committee on Vital and Health Statistics, views the development of 

hospital data in the United States and discusses how they may be used 

for epidemiologic studies of chronic disease, for disease surveillance 

purposes, and for medical-care research. The full potential of morbidity and other data in hospital records needs to be exploited for 

epidemiologic and medical-care research. 

Robert L. Berg, M. D., Chairman 

U.S. National Committee on 

Vital and Health Statistics 

... Ill 
U.S. NATIONAL COMMITTEE ON VITAL AND HEALTH STATISTICS 

Robert L. Berg, M. D., Chairman


Professor and Chairman, Department of


Preventive Medicine and Community Health


The Medical Center


The University of Rochester


Rochester, New York


Iwao M. Moriyama, Ph. D., Executive Secretary


Director, Office of Health Statistics Analyais


National Center for Health Statistics


Public Heslth Service*


Washington, D.C.


Donald J. Davids


Chief, Records and Statistics Section


Colorado State Department of Public Health


Denver, Colorado


Clyde V. Kiaer, Ph.D.


Senior Member, Technical Staff


Milbank Memorial Fund


New York, New York


Herbert E. Klarman, Ph.D.


Department of Public Health Administration


School of Hygiene and Public Health


The Johns Hopkins University


Baltimore, Maryland


SUBCOMMITTEE ON EPIDEMIOLOGIC 

Paul M. Denaen, SC.D., Chairman 

Director, Center for Community Health 

and Medical Care 

School of Public Health and Medical 

School


Harvard University


Bostcm, Msssachuaetts “


Warren Winkelstein, Jr., M. D., Secretary


Professor, Department of Epidemiology


School of Public Health


University of California


Berkeley, California


Jacob E. Bearman, Ph.D.


Professor, Biometry Division


School of Public Health


College of Medical Sciences


University of Minnesota


Minneapolis, Minnesota


Alexander D. Langmuir, M.D,


Chief, Epidemiology Program


National Communicable Disease Center


Health Services and Mental Health


Administration, Public Health Service*


.4tlanta, Georgia


Charles E. Lewis, M.D.


Professor and Chairman, Department of


Preventive Medicine and Community Health


University of Kanaas Medical Center


Kansas City, Kansas


Forrest E. Linder, Ph.D.


Department of Biostatistics


School of Public Health


University of North Carolina


Chapel Hill, North Carolina


Robert Parke, Jr.


Program Planning Officer


Bureau of the Census


U.S. Department of Commerce


Washington, D.C.


John R. Philp, M.D.


Health Officer


County of Orange Health Department


Santa Ana, California


Donovan J. Thompson, Ph.D.


Department of Preventive Medicine


School of Medicine


University of Washington


Seattle, Washington


Theodore D. Woolsey, ex officio


Director, National Center for Health Statistics


Public Health Service* 

Washington, D.C. 

USE OF HOSPITAL DATA 

Alfonse T. Masi, M. D., Dr.


Department of Medicine


The University of Tennessee


Memphis, Tennessee


Robert W. Miller, M.D.


Chief, Epidemiology Branch


National Cancer Institute


National Institutes of Health


Public Health Service*


Bethesda, Maryland


Robert Ivf. Sigmond


Executive Director


P.H. 

Hospital Planning Association of 

Allegheny County 

Pittsburgh, Pennsylvania 

Vergil N. SIee, M.D. 

Director, Commission on Professional and 

Hospital Activities 

Ann Arbor, Michigan 

Paul F. Wehrle, M.D.


Chief Physician


Pediatrics and Communicable Disease


Services


Los Angeles County General Hospital


Los Angeles, California


*Depmtmentof Health, Education, nnd Welfare. 

iv 
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CONTENTS 

Foreword 

Introduction


Epidemiologic Research


Retrospective (case-control) Studies


Prospective (cohort) Studies


Epidemiologic Surveillance


Medical-Care Research


Influence of Dia~oses Per Se-----------------------------------------


Influence of Organizational Structure for Providing Medical Care and


of Type of Physician


Influence of the Physician's Characteristics


Influence of Various Types of Case Management


Confidentiality


References


... m 

1 

1 

2 

3 

5 

6 

6 

7 

7 

7 

8 

8 

v 
IN THIS REPORT a Subcommittee of the U.S. National Committee on 

Vital and Health Statistics considers the potential value, the available 

methods, and the problems of using hospital data fov epidemiolo~”c 

studies. 

Increasing standardization of diagnostic procedures improves the reliability of hospital diagnoses. Increasing utilization of hospitals veduces 

the difference between the medical expedience of the hospitalized and 

the geneval populations. Both trends enhance the potential of hospital 

data fov epidemiolo~”c study. Hospitil vecovds provide access to large 

num km of cases of specific diseases which would be difficult to identify 

in general population suvveys. 

Techniques ave descvibed, pvoblems are identified, and examples ave 

given for several types of hospital studies: ~etvospective (usually casecontrol) studies of specific diseases or conditions; prospective (coho~t) 

studies with either analytical or clinical- tvial objectives; disease surveillance intended to identify changes in levels of incidence; and medical- care veseavch which is concerned with relationships between 

utilization and the chavacte-vistics of physicians, hospitals, and case 

management as well as the specific diagnosis. 

Opportunities fov hypothesis testing ave pointed out, along with ~equivements, in terms of procedures for vecovding data and the selection of 

conhol groups. 

vi 
USE OF HOSPITAL DATA FOR EPIDEMIOLOGIC


AND MEDICAL-CARE RESEARCH


INTRODUCTION 

At the suggestion of the Epidemiology Section 

of the American Public Health Association made 

during its 1964 meeting in New York City, the 

Subcommittee on Epidemiologic Use of Hospital 

Data was constituted by the U.S. National Committee on Vital and Health Statistics. The task of 

this Subcommittee was to make a study of the uses 

of diagnostic and other data on hospital patients, 

including statistics needed for epidemiologic and 

medical-care research, studies of current therapeutic practices, and for health surveillance. 

With the increased standardization of diagnostic tests and criteria, hospital data have become more reliable in recent years. The fact that 

the general hospital is being regarded more and 

more as the hub of a complex of facilities providing medical care—inpatient and outpatient, preventive and curative—increases the possibility y 

that hospital data will provide a useful indicator 

of the medical experience of the general population. This opens up the possibility of utilizing diagnostic information in hospital records for purposes other than the treatment of patients. Indeed 

the subcommittee believes that the full potential 

of information in hospital records has yet to be 

exploited. 

The major advantage presented by such data 

lies in the ready accessibility of large numbers of 

cases of specific illnesses. To exploit this advantage to the full, it is essential that rigorous scientific procedures be followed. 

In this report hospital refers to the shortterm general hospital. It is recognized that additional studies of data from chronic disease and 

psychiatric hospitals and from nursing homes 

will sometimes be necessary because short-term 

general hospitals are utilized primarily by patients with acute illnesses and with surgical problems. 

The three areas in which the information in 

hospital records can contribute are epidemiologic 

research, disease surveillance, and medical-care 

research. Each of these areas will be briefly reviewed with respect to the role of the hospital 

record. 

EPIDEMIOLOGIC RESEARCH 

While data on hospital patients have, in the 

past, provided a resource for testing hypotheses 

on disease causation, it is anticipated that this 

resource will be increasingly useful in the future. 

This is due to the increasing availability of hospital care through the extension of private and 

governmental support as well as to the increased 

recognition of the hospital as a technological 

center. Masil has pointed out the potential uses 

of hospital data for epidemiologic research as 

well as their limitations. While some problems 

attend the use of hospital data for epidemiologic 

purposes, the availability of these data as well 

as their comprehensive nature suggest that their 

use be fully exploited. 

The two approaches to the epidemiologic testing of hypotheses are (1) the retrospective or 

case-control method and (2) the prospective or 

cohort method. In general, findings of retrospective studies will need to be extended by the appli1

cation of more rigorous designs based on either 

community population samples or on prospective 

studies of carefully defined hospital patients and 

controls. Prospective studies may be regarded as 

more definitive testing of hypotheses. 

Retrospective (case-control) Studies 

Retrospective (case-control) studies can proceed along either of two lines —namely, one in 

which cases and controls are both drawn from the 

hospital population or one in which cases are 

drawn from a hospital population and controls 

from nonhospital populations or the community 

at large. 

Cases and contvols jrom hospital populations. —Several studies in which both cases and 

controls were derived from hospital populations 

are available for comment. These studies usually 

involve diseases which cause the majority of patients with the diseases to be hospitalized and 

which can be diagnosed using fairly standard and 

reproducible criteria, e.g., lung cancer,2 sarcoidosis,3 and Hashimoto’s disease.4 

The usual method of conducting a retrospective study involves identifying a sample of patients 

with the diagnosis and subsequently obtaining relevant information regarding the characteristics of 

these patients. A control sample is obtained from 

patients with other diagnoses, and the frequency 

of the characteristics under study is compared in 

the two groups. A classic example of such a study 

was reported by Levin and others2 and was concerned with the relationship between cancer of 

certain sites and tobacco smoking. The investigators routinely obtained a history of tobacco usage 

from all patients admitted to the Roswell Park 

Memorial Institute, a cancer research hospital, 

beginning in 1938 and showed an association between cigarette smoking and cancer of the lung 

and between pipe smoking and cancer of the lip. 

This study clearly demonstrated the following advantages of using data on hospitalized patients for 

retrospective epidemiologic study: 

a.	 Availability of a large number of cases of 

a particular disease and of suitable controls for comparison analysis. 

b.	 Possibility of collecting information on 

independent variables of interest such as 

smoking from cases and controls. 

c.	 High degree of diagnostic accuracy in 

defining case and control populations. 

On the other hand, this study also illustrated 

some of the problems which have been cited in 

connection with the use of hospital populations. 

a.	 Hospital detected cases may not be inclusive and are subject to selection according to factors such as socioeconomic 

status, severity of disease, and psychological and culturally determined attitudes 

of the hospital patient. 

b.	 Because of the selection referred to, the 

population base furnishing the cases cannot be precisely defined. 

c.	 Most hospital records are not designed 

with research uses in mind. The records 

are frequently incomplete and the approaches to data collection are not standardized. Further, there is considerable 

variability between hospitals in diagnostic 

accuracy and reproducibility. However, 

such difficulties may be minimized in a 

research institution like the Roswell Park 

Memorial Institute, where the record system and the clinical activities may be 

subjected to the control of the research 

staff. In other situations, research uses 

may be expected to promote standardization and improvement in quality. 

The most serious criticism of the type of 

study outlined above is that the hospital admission 

rates for each of the designated disease groups 

(cases and controls) may be different and may be 

related to the independent variable under study. 

Berkson5 has discussed this problem and has delineated the conditions under which valid comparisons may be made. If unequal admission rates 

are unrelated to the independent variable under 

study, then comparisons of the diagnostic groups 

can be made without bias. The problem is to determine whether or not the independent variable 

affects the admission rate. This determination is 

not always possible, but it must always be attempted. 

Cases from hospital populations and controls 

from nonhospitulized populations, -There are 

several ways of guarding against the possibility y 

of error from unrepresentativeness of controls, 

2 
Among them is the selection of hospital case 

controls from a wide variety of diagnoses so that 

possible hidden factors of bias related to certain 

diagnostic categories will be diluted. Another approach is to draw the control sample from the 

general population usually by one of two methods. 

The first is to obtain a matched sample by controlling on a number of standard variables such 

as age, race, and economic status. The second, 

and preferable approach, is to obtain a random 

sample of the population and then to match it to 

the sample. The advantage of the latter is that one 

can get frequency estimates of the independent 

variables of interest in the population at large 

and compare them with both the matched control 

sample and with the case group. Both of these 

methods were used in a study of pregnancy wastage and coronary artery disease in females by 

Winkelstein and others.6 These investigators obtained a case population of women who had survived a myocardial infarction and compared their 

pregnancy patterns with a matched sample of 

women drawn by canvassing houses adjacent to 

the residences of the cases and matching on age, 

race, and marital status. A second control was 

obtained from a random sample of the population 

surveyed for other purposes, which also provided 

complete information on pregnancy experience. 

These findings indicated that there was about 

twice as much pregnancy wastage among the cases 

of myocardial infarction as among either matched 

controls or controls drawn from the population 

sample, A difficult problem to overcome in this 

type of study is the difference in recall for the 

characteristic under consideration between hospitalized patients and population controls. Furthermore, it is difficult to hide from the interviewer the identity of the cases as contrasted with 

the controls. 

The advantage of this type of retrospective 

design is apparent when dealing with diseases of 

low prevalence in the population. Under such circumstances it is usually difficult, if not impos ­

sible, to identify cases from a population sample; 

therefore, reliance must be on hospital data for 

the initial recruitment of the case population. 

Prospective (cohort) Studies 

Analytic studies. —A prospective hospitalbased analytic study differs from the retrospec ­

tive study in that data are collected according to 

a defined protocol on a defined cohort. In the prospective study the investigator begins with a hypothesis and designs a protocol to collect systematically the history, physical examination data, 

and laboratory data necessary tb test the hypothesis. Thus, the fullest control can be exercised 

in collecting the required information. However, 

there may be selection in the hospitalized segment 

of the total cases in the community depending upon 

the hospital utilization pattern for any disease. 

Examples of some prospective controlled epidemiologic studies conducted in hospitals will illustrate some of these points. 

A study of viral hepatitis in a group of Boston 

hospitals highlights the transition from a retrospective to a prospective analysis of hospital data 

as well as the increased power of the prospective 

study design. After a retrospective review of hospitalized hepatitis patients, Grady and Chalmers7’8 designed a prospective study in 1963, involving 10 Boston hospitals, to determine whether 

hepatitis patients had different types of exposures 

than matched controls. Biweekly visits were made 

to each of the participating hospitals. Included in 

the study were patients over 15 years of age with 

a working diagnosis of hepatitis. These patients 

were given a standard questionnaire which included questions about personal contact with other 

hepatitis patients, possible anicteric cases, travel, eating habits and places, parenteral exposures, 

and transfusions. The same questionnaire was 

given to paired controls. The controls were 

matched by age, race, sex, marital status, hospital 

pay status, and date of admission. They were previously healthy persons admitted for incidental 

surgery, e.g., fractures and appendicitis. 

The findings from the study showed that hepatitis patients who had not recently been transfused had a significantly larger consumption of 

raw clams and oysters than the controls. These 

cases had also received more injections from 

physicians. Some other factors such as dental 

procedures and exposure to certain insects showed 

no differences. Thus, some of the exposures 

previously suspected of leading to hepatitis were 

confirmed in this study, and others such as exposure to cockroaches and dental procedures, 

which were also suspected on clinical inference, 

were clearly excluded. 

3 
As a byproduct of the smdy, it was found 

that there were quite distinctive clinical features 

for cases of hepatitis transmitted through the 

parenteral and oral routes. Rigorously controlled 

analytic prospective epidemiologic studies offer 

opportunities such as this to describe more precisely the pattern of disease because it is necessary to define and categorize cases prior to the 

study. 

In another analytic prospective hospitalbased study, the National Center for Radiological 

Health of the Public Health Serviceg is conducting 

a cooperative multihospital followup of some 

40,000 adult patients with a history of thyrotoxi ­

cosis, About three-fourths of these patients had 

radioactive iodine treatment for thyrotoxicosis, 

and the remainder had surgery. Both groups are 

being followed biannually according to a specified 

protocol. The main objective was to determine if 

there were more complications (e.g., blood dys ­

crasias or thyroid cancer among the radioactive 

iodine treated patients) than would be expected 

from the experience among surgically treated 

controls which might be attributable to radiation 

exposure. Since no treatments were imposed on 

either the case or control groups, this was an 

observational analytic study. A systematic followup is being made to determine any differences in 

outcome. 

As with retrospective studies, concern in 

prospective studies must be with the selection of 

patients and the possibilities of spurious associations. Generalization of the conclusions is, of 

course, strictly limited by the sample of patients 

coming to the hospital in terms of the severity of 

disease and other selective factors. 

The difference between an epidemiologic 

study and a clinical study sometimes becomes 

hazy. If the major purpose of an investigation is 

to test a hypothesis using case and control populations or to derive comparative prevalence and 

incidence rates in a defined population, it may be 

said that the study is epidemiologic. On the other 

hand, a descriptive study of diseases not involving 

any hypotheses or a control population is a clinical study. With increasing collaboration between 

clinicians and epidemiologists, the difference becomes unimportant. What is important is to employ epidemiologic methods that are effectively 

consistent with statistical theory and clinical 

technology for the conduct of studies that have the 

greatest potential for improving our knowledge 

for reducing illness, disability, and mortality, and 

for improving the prognosis of the patients. 

Clinical tvials. —A particular class of prospective study is that which deals with the testing 

of the relative efficacy of certain forms of therapy, including drugs and vaccines. As with retrospective studies, concern must be with the problems of selecting patients and the possibilities of 

spurious association. As in many experimental 

studies, however, the risk of shortcomings using 

hospital patients is diminished wherever treatments can be randomly assigned. The generalization of conclusions is, of course, limited to the 

nature of the hospital population in terms of diseases, their severity, and other selective factors. 

However, for the purposes of certain treatments, 

there may be little reason to suspect that there 

will be a significant difference in effect between 

nonhospital cases and hospital patients. For 

example, if aspirin can be shown to be effective 

in treating rheumatoid arthritis in hospital patients, is there any reason a priori for thinking 

that the nonhospital sample would respond differently? This is analogous to the dilemma of 

using volunteers in a vaccine field trial. Volunteers of certain age, race, and sex with a particular socioeconomic or educational background 

may possibly react differently to a vaccine than 

would members of the entire community. Nevertheless, if the vaccine shows a high degree of 

efficacy in the test group, it should also prove to 

be effective when applied to the whole community. 

An example of a study in this area is the one 

conducted by Chalmers and others 10 on veterans 

of the Korean war, where hepatitis patients were 

randomly assigned to one of four hospital wards 

identical in all aspects of management except for 

a single factor of treatment. Systematic evaluation of the patients over the short term of several 

months revealed no differences in the outcome, 

regardless of the treatment regimen. A 10-year 

followup of the majority of these patients showed 

no adverse effects, which could be attributed 

either to type of exercise or to dietary regimen. 11 

More recently, Garceau and others12 in a coordinated study of 10 Boston teaching hospitals 

comprising the Boston Inter-hospital Liver Group 

tested the efficacy of surgery versus conserva4 

1 
tive management of portal hypertension. Patients 

with liver cirrhosis who fulfilled certain physical 

and laboratory criteria were invited to participate in the study knowing that they would have a 

random chance of being selected for surgery or 

for medical management. This study was important because the criteria for eligibility for surgery 

were defined prior to the study, and eligible volunteers were randomly assigned to this category. 

Although patients who were randomly picked for 

surgery did better than those who were not eligible 

for surgery because of medical contraindications, 

they did no better than the comparison group—the 

patients randomly assigned to conservative management. If a rigorous study method can be applied 

to a procedure as major as portacaval shunt surgery in a disease as variable and potentially life 

threatening as advanced liver cirrhosis, then this 

approach can also be applied to most therapeutic 

questions in medicine. The most important factor 

is a dedication to discover the true answer to a 

therapeutic dilemma. As long as the dilemma 

exists and the patient is frankly informed of his 

or her risks and the alternatives, then there is 

little or no infringement of personal or professional ethics in conducting such studies. Rather 

the investigator should try to discover the answer 

to such questions as soon as possible in order to 

provide all patients with the preferred therapy 

and to spare many a needless procedure. 

Currently a long-term, collaborative interhospital drug trial is being started to test the 

efficacy of various medications on the treatment 

and survival of patients with coronary heart dis -

ease. Is More than 8,400 patients in 50 clinics 

across the country will be involved. 

Certain coronary patients will receive one of 

four drugs or a placebo to evaluate their ability 

to prevent recurrence of myocardial infarction. 

This prototype of a drug-trial study has unlimited 

potential for determining the effects of drugs, and 

it represents a fertile field of mutual endeavor 

for epidemiologists, statisticians, and clinicians. 

Mainland and Sutcliffe 14’15 have provided 

magnificent examples of experimental studies of 

arthritis among hospital outpatients. In these 

studies the Cooperating Clinics Committee of the 

American Rheumatism Association is engaged in 

testing the efficacy of various medications on the 

course of rheumatoid arthritis. The effect of aspirin was studied in a systematically controlled 

fashion, and, in turn, the effect of other medications will be compared with it. 

The same theory that applies to inpatients 

would apply to outpatient populations whether they 

be individuals attending a clinic or occupational 

groups enrolled in hospitalization programs. 

Another possibility not developed in this report 

because of the paucity of published reports is the 

potential of using Blue Cross records and similar 

hospital insurance programs as a source of cases 

and controls. It is hoped that eventually these records can be used prospectively to determine 

comparative morbidity in a study of disease associations or possibly for confirming high-risk 

morbidity groups identified through independent 

sources. 

EPIDEMIOLOGIC SURVEILLANCE 

The existing system of epidemiologic surveillance based primarily on the reporting of notifiable diseases by physicians is not satisfactory 

because of the gross incompleteness of reporting 

and the limited nature of coverage of disease 

problems. The diagnostic data in hospital records 

should provide a particularly useful source of information for detection of sudden changes in morbidity. 

The key to this problem is to develop casefinding methods which would provide the needed 

data and at the same time overcome the problem 

of time lag inherent in discharge data. In some 

instances admission diagnoses could alert the 

health official to the need for thorough investigation. Another possibility would be to assign theresponsibility to an epidemiologic officer16’17 within 

the hospital who could experiment with the most 

effective means of finding cases of public health 

concern. 

In the use of hospital records, care must be 

taken to avoid erroneous conclusions due to errors 

or incompleteness in the observations recorded. 

In surveillance as in the hypothesis-testing use of 

hospital records, the observer must not confound 

differences of etiologic significance with results 

arising from the fact that patients choose hospitals or are referred to hospitals in nonrandom 

fashion. Undue concern with this bias has, in recent years, resulted in the underutilization of hos -

5 
pital records as a source of information of great 

potential value. 

Problems are also to be expected in the estimation of the incidence and prevalence of various 

diseases. Estimates based on hospital admissions 

will be less valid for chronic diseases than for 

illnesses characterized by a single acute attack 

that requires hospitalization and results in immunity of long duration. Furthermore, the use of 

in-hospital data will cause the loss of large numbers of acute and minor diseases which are diagnosed and treated in physicians’ offices or in 

outpatient departments. 

It is recognized that the reporting of diseases 

and preliminary y diagnoses by one hospital or by 

a few hospitals in a large metropolitan area would 

be of limited value because patients choose or are 

referred to hospitals in nonrandom fashion. Bias 

introduced in this way could lead to differences 

which would suggest spurious etiologic relationships. However, undue concern with such possibilities in recent years has led to hospital records 

being underutilized as a valuable source of information. These risks would be greatly reduced 

if all hospitals in a metropolitan area or other 

defined geographic area would join in a common 

computer service for broad administrative and 

fiscal purposes; this would make possible the systematic collection of admission and discharge 

diagnoses that would have maximal value for 

epidemic surveillance. 

MEDICAL-CARE RESEARCH 

The use of hospital data for purposes of 

medical-care research is comparable to its use 

for epidemiologic purposes. However, rather than 

to identify the characteristics of patients with 

specific diseases, the goal in this case is to identif y the characteristics of patients who seek various care and to determine the effect of organizational and professional characteristics of the 

hospital on receipt of care. Such information suggests hypotheses as to why certain patients do or 

do not receive care and why such care may be 

costly. In this case the hospital also provides a 

resource for testing hypotheses. 

Obtaining medical care is greatly influenced 

by the disease process, including symptoms and 

severity, as well as by such demographic characteristics of the patient as age and sex. Therefore, 

interpretation of utilization patterns must also 

take into account diagnoses and associated disabilities. Such diagnostic information is usually 

more accessible and reliable when obtained from 

hospital records than from other sources. The 

uses of these data are discussed below under 

four headings, each of which represents a major factor influencing patterns of hospital utilization. 

Influence of Diagnoses Per Se 

For this purpose discharge data by diagnostic 

categories are useful. Data for a specific hospital 

may be of value to the hospital itself in evaluating 

its functions and in servicing the community. 

However, these data are usually of limited value 

for any one hospital in the community since the 

population served by a given hospital is ordinarily 

difficult to delineate. If all hospitals in the community are included, discharge data for residents 

of that community and the population estimates 

for the total community may be used to establish 

discharge rates. 

Diagnostic data for the country as a whole 

are available from the Hospital Discharge Survey 

of the National Center for Health Statistics, which 

is a probability sample of U.S. hospitals .Is!lg For 

smaller areas such as States and metropolitan 

areas, corresponding data are not routinely tabulated. There are, however, collection mechanisms 

in existence which do have the potential for providing such data for a sizable and definable population subgroup. Among such mechanisms are the 

Blue Cross and/or commercial hospital insurance 

programs and certain group practice programs 

such as the Health Insurance Plan of Greater 

New York20”22 and the Kaiser- Permanence Program in California. 23 In addit ion, the Professional 

Activity Study at Ann Arbor Michigan, insofar as it 

serves hospitals in several areas, might provide 

similar information. Data potentially available 

from social programs such as Medicare and Medicaid may also be used for this purpose. In Allegheny County, Pennsylvania, the Blue Cross has a 

program which provides a continuous “patient register” and r-elated statistical tabulations for each 

hospital. 

6 
In many of these medical-care programs, the 

diagnostic data become available as part of a system designed to pay claims or for some other administrative reason. In others it will be necessary 

to code a sample of the records. In such cases it 

is desirable that the diagnostic tabulations have 

some meaning in terms of the organization’s own 

purposes in order to justify the sizable expense 

represented by such procedures. 24 

Influence of Organizational Structure for 

Providing Medical Care and of Type of 

Physician 

It has been shown that hospitalization rates 

for members of group practice programs are 

lower than those for comparable groups serviced 

by other programs or for groups seeking care independently. 20-22 The differences, however, are 

not uniform for all diagnostic categories. For 

example, the difference in hospitalization rates 

between individuals served by group and by nongroup programs is greater for patients with tonsillectomies and adenoidectomies than for those 

with neoplasms. Such knowledge is of considerable 

importance in planning a framework by which 

medical services are made available to the population. Moreover, since the population is given a 

choice of several different kinds of medical-care 

programs (as is the case in the Medicaid program 

in New York City), it is of more than passing interest to examine the utilization patterns by diagnosis among the several plans. Differences in 

patterns after appropriate adjustments for population characteristics may yield clues as to differences in medical practice which may, in turn, 

suggest ways of examining the quality of medical 

care in different settings. 

Discharge rates by diagnoses are required 

for the study of this problem, and they need to be 

classified as follows: 

1.	 Type of practice of physician discharging 

the patient 

a. Solo 

b. Partnership 

c. Group practice 

d. Hospital-based 

2.	 Type of hospital from which patient was 

discharged 

a. AHA accredited or nonaccredited 

b.	 Teaching or nonteaching or university 

or nonuniversity 

c.	 Auspices (voluntary, proprietary, governmental) 

d.	 Type of outpatient department organi ­

zation (speciality clinics only, general 

medical or speciality clinic, and other) 

Various cross-classifications of these and 

other variables may also be desired. Such classifications require that the necessary information 

be available on the discharge report and appropriately coded. 

Influence of the Physician’s Characteristics 

The following classification of the physician’s 

professional characteristics is suggested: 

1.	 Physician specialty (general practitioner, 

internist, pediatrician) 

2. Years since graduation 

3.	 Type of staff appointment (none, courtesy, 

active, consultant) 

Again some degree of cross-classification 

may be desired. 

In this connection, it would be helpful if each 

physician in a community was assigned a code 

number, as was done in Allegheny County, Pennsylvania. The code number would identify his type 

of practice, specialty, board certification, age, 

and other factors. It would permit grouping of 

data from various locations—either by physician 

or by physician characteristics. It would also permit comparisons of the behavior of the same physician in different settings. 

Influence of Various Types of Case 

Management 

The concept of progressive patient care has 

given rise to a variety of different methods of 

case management. Since the diagnosis is clearly 

one of the determinants of case management, one 

may raise the question of whether subsequent experience of a patient with a particular diagnosis 
varies with different methods of case management. Subsequent experience may be measuredin 

many ways, such as readmission rates during a 

given period after initial discharge,length of time 

required to return to work, and subsequent use of 

physician’s or nurse’s services. These data will 

not necessarily be available from a routine reporting system. It may be necessary to do a followup on the patient and to obtain information by 

direct interview. These data may then be correlated with the presence or absence and use ofi 

1. Formal intensive care unit in the hospital 

2. Home care program 

3.	 Nursing home affiliation by type of affiliation 

4. Formal discharge planning program. 

It will be essential in carrying out such studies to have detailed knowledge of the criteria for 

admission to a particular kind of case-management program. A control or comparison group is 

also needed. In general, the requirements for 

more definitive study here are similar to those 

in the discussion of hypotheses testing under 

Prospective Studies. 

CONFIDENTIALITY 

A problem which has been raised recently in 

some of the epidemiologic studies utilizing hospital data has been that of confidentiality and privileged communications. This issue involves the 

relationship between the hospital staff physician 

and the patient. In some States much of the infer. 

mation, particularly the diagnosis, obtained aml 

recorded in the hospital records is of a privileged 

and confidential nature .25 Making such information available for epidemiologic purposes is considered by some to be a violation of trust. Thus, 

it is sometimes necessary to obtain the permis ­

sion of every patient whose record is to be used. 

It is obvious that this can be a cumbersome and 

difficult process. 

In some instances, special legislation has 

been passed permitting the use of hospital data for 

such purposes as medical audits. New York State 

has recentIy enacted legislation which gives the 

State health officer access to individual records. 

Edgar S. Dunn26 has stated that it is necessary to distinguish clearly between intelligence 

data about individuals as individuals, such as medical records a doctor keeps to trace changes in the 

wellbeing of his patients, and statistical data that 

relate to groups of individuals. Statistical data 

are concerned with aggregates, averages, percentages, and so forth that describe relationships 

characteristic of groups of, for example, hospital 

cases. No personal information about the individual needs to be available to anyone other than 

those engaged in the research. Respect for confidentiality of medical information has been characteristic of epidemiologic studies. The need for 

the protection of an individual’s privacy is well 

appreciated and understood by individual researchers, and specific steps are usually taken 

to provide the necessary protection. 
lMusi, A. T.: Potential uses and limitations of hospital 

dutu in epidemiologic researoh. Am. J. Pub. HeaZth 55(5):658-

OW1 May 1965. 

‘Lovin, hf. L., Goldstein, H., and Gerhardt, P. R.: Cancer 

and tobacco emoking. J.A.M .A. 143(4):336-338, hiay 1950. 

‘lBuck, A. A.: Epidemiologic investigations of sarcoidosis. 

.bn.J.Hg:7. 74(2):137-202, Sept. 1961. 

lhf,lqi A. T., and others: Hashimoto’s disease, a clinicopntholo~i;til study with matched controls. Lancet 1 (7377 ):123-

lW, Jun. 1966. 

‘iBerkson, J.: Limitations of the application of four-fold 

table analysis to hospital data. Biometrics 2:47-53, 1946. 

‘iWink@lstein, W., Jr., Stenchever, M., and Lilienfeld, 

A. M.: Occurrence of pregriancy, abortion and artificial menopauso among women with coronary artery disease, a preliminary study. J. C/won .DLs. 7(4):273-286, Apr. 1958. 

7Grndy,. G. F., Chalmers, T. C., and the Boston Inter-Hospital Liver Group: Viral hepatitis in a group of Boston hospitals-I. A retrospective study of 1675 patients. New EngZund 

,J. Mcd, 272(1:3):657-661, Apr. 1965. 

8@ndY, G. F., Chalmers! T. C., and the Boston Inter-Hospital Liver Group: viral hepatitis in a group of Boston hospituls-H. A prospective controlled epidemiologic study. New 

Entiltmd J.Mcd. 27’2(1 3):662-666, Apr. 1965. 

0?

hnongcm, E. L., Thoma, G. E., and Tompkins, E. A.: Inrirlonce of leukemia following treatment of hyperthyroidism, 

u ptwliminnry report of the Cooperative Thyrotoxicosis Therups Follow-up ‘Study. J.A.M .A. 205(1 2):855-862, “Sept. 1968. 

l%hulmers, T. C., and others: The treatment of acute infm-tious heputitis, controlled studies of the effects of diet, 

r,,st,, [lnd physical reconditioning on the acute course of the 

disuaso and on the incidence of relapses and residual abnormuliticw. ,J.Clin.invest. 34(7):1163-1235, July 1955. Part II. 

11Chulmers, T. C., and Nefzinger, M. D.: The treatment of 

acwto infections hepatitis, 10-year followup study. Gastrornfmdogy 42:479, 1962. (abstract) 

12Gnrcewr, A. J., the Boston Inter-Hospital Liver Group, 

and others: A controlled trial of prophylactic portacaval-shunt 

surgery. Now EngZand J.Med. 270(10):496-500, Mar. 1964. 

1:3National Heart Institute. The Co Tonary Drug Project. 

PHS Pub. No. 169+5. National Institutes of Health. Washing 

ton. LI.s. Government Printing Office, 1967. 

14Mainland, D., and Sutcliffe, M. I.: Aepirin in rheumatoid arthritis, n seven-day double-blind trial-preliminary report. J3u11.EJteumat. Dis. 16:388-391, NOV. 1965. 

15Cooperating Clinics Committee of the American Rheumatism Association: A seven-day variability study of 499 

patients with peripheral rheumatoid arthritis. Arthrctis Rheumat. VIII(2) :302-335, Apr. 1965. 

16 Fuerst, H. T., and Lichtman, H. “S.: Directions in hospital epidemiology. New York J.Med. 66(10):1202-1205, hfay 

1966. 

17Lichtman, H. S., and Stuart, G. M.: The Community Oriented Hospital Epidemiologist. Paper prepared for presentation at the 93d annual meeting of the Epidemiology Section of 

the American Public Health Association, Oct. 21, 1965, Chicago, 111. 

18Sirken M. G.: The hospital discharge survey. Pub. Hea2th 

Rep. 82(1):9-16, Jan. 1967. 

19National Center for Health “Statistics: Patients discharged from short-stay hospitals, United States, OctoberDecember 1964, Vital and Health Statistics. PHS Pub. No. 

1000J3eries 13-No. 1. Public Health ‘Service. Washington. 

U.S. Government Printing Office, Oct. 1966. 

20Densen, P. hi., and others: Prepaid medical care and 

hospital utilization. American Hospital Association. Chicago 

Hospital Monograph ‘Series No. 3, 1958. p. 55. 

21Densen, P. M., Jones, E. W., Balamuth, E., and ‘Shapiro, 

S.: Prepaid medical care and hospital utilization in a dual 

choice situation. Am. J. Pub. HeaZth 50(1 1):1710-1 726, Nov. 

1960. 

22 Densen, P. M., Shapiro, “S., Jones, E. W’., and Baldinger, 

1.: Prepaid medical care and hospital utilization, Comparison 

of a group practice and a self-insurance situation. HospitaZe 

36(22):62, iiov. 1962. 

23\veissman A .: A morbidity study of the Permanence 

Health Plan population. Pe~manente Found.,41.BuU. X(1-4):12-

26, Aug. 1952. 

24 Densen, P. M., and Shapiro, “S.: Methodological probleme 

in the study of special population groups, health insurance 

and industrial groups. Ann. New York Acad.Sc. 107(2):490-

505, May 1’963. 

2~ayt. E., and Hayt} J.: Legal Aspects of Medical Records. Berwyn, 111. Physicians’ Record Company, 1964. pp. 74, 

75, 93. 

26U .’S. Congress, House Committee on Government Operations: The computer and invasion of privacy. Hearings before 

a subcommittee of the Committee on Government Operations, 

House of Representatives, 89th Congress, July 26-28, 1966. 

Washington. U.S. Government Printing Office, 1966. p. 92. 

000 

~ “, .s. GOVERNMENT PRINTING oFFIC= 19 S9—3~2049/!54


9 
OUTLINE OF	 REPORT SERIES FOR YITAL AND HEALTH STATISTICS 

Public Health Service Publication No. 1000 

SeTies 1, 

Sevies 2. 

Sevies 3. 

Series 4. 

Sevies 10. 

Series 11. 

Sevies 12. 

SeVies 13. 

Series 14. 

Series 20. 

SeYies 21. 

Series 22. 

P~o,gvams and collection pvoceduves.— Reports which describe the general programs of the National 

Center for Health Statistics and its offices and divisions, data collection methods used, definitions, 

and other material necessary for understanding the data. 

Data evaluation and methods ~esea?’ch. —Studies of new statistical methodology including: experimental tests of new survey methods, studies of vital statistics collection methods, new analytical 

techniques, objective evaluations of reliability of collected data, contributions to statistical theory. 

Analytical studies. — Reports presenting analytical or interpretive studies based on vital and health 

statistics, carrying the analysis further than the expository types of reports in the other series. 

Documents and committee Yeports. — Final reports of major committees concerned with vital and 

health statistics. and documents such as recommended model vital registration laws and revised hi rth 

and death certificates. 

Data fYom t}ze Health Inte%,zjzew SuYveY. —Statistics on illness, accidental injuries, disability, use of 

hospital, medical, dental, and other services, and other health-related topics, based on data collected 

in a continuing national household interview survey. 

Data from the Health Examination Sur~e~. — Data from direct examination, testing, and measurement of national samples of the population provide the basis for two types of reports: (1) estimates 

of the medically defined prevalence of specific diseases in the United States and the distributions of 

the population with respect to physical. physiological, and psychological characteristics; and (2) 

.malysis of relationships among the various measurements without reference to an explicit finite 

universe of persons. 

Data fvom the Institutional Population %~veys. — Statistics relating to the health characteristics of 

persons in institutions, and on medical, nursing, ~nd personal care received, based on national 

samples of establishments providing these services and samples of the residents or patients. 

Data fvorn the Hospital Dischavge Suwey. —Statistids relating to discharged patients in short~stay 

hospitals, based on a sample of patient records in a national sanlPle of hospitals. 

Data on health ~esouvces: rnanpowev and facilities. —Statistics on ihe numkrs, geographic” distribution, and characteristics of health reso~rces including physicians, dentists, nurses, other health 

manpower occupations, hospitals, nursing homes, and outpatient and other inpatient facilities. 

Data on mortality. -Various statistics on mortality other than as included in annual or monthly 

reports —special analyses by cause of death, age, and other demographic variables, also geographic 

and time series analyses. 

Data on natality, rnarviage, and diuo?’ce. —Various statistics on natality, marriage, and divorce other 

than as included in annual or monthly reports—special analyses by demographic variables, also 

geographic and time series analyses, studies of fertility. 

Data fro”rn the National Natality and Mortality Su)’ueys. —Statistics cm characteristics of births and 

deaths not available from the vital records, based on ‘sample surveys stemming from these records, 

including such topics as mortality by socioeconomic class, medical experience in the last year of 

life, characteristics of pregnancy, <>tc. 

For a list of titles of reports published in these series, write to: Office of Information 

National Center for Health Statistics 

U.S. Public Health Service 

Washington, D.C. 20201