Journal of Community Health Vol. 4, No. 2, Winter 1978
EPIDEMIOLOGICAL
APPLICATIONS SERVICES
TO
HEALTH
RESEARCH
B a r b a r a S. Hulka, M.D., M.P.H.
ABSTRACT: A model is presented to illustrate some areas in which epidemiological thinking may be applied to health services research. The model is neither exhaustive nor exclusive, for other areas not specifically described as within the model are also a part of the domain of epidemiology, and several aspects of the model are shared with researchers in other disciplines. Selected examples of epidemiological applications are reviewed; these include: (1) the need for health care services, (2) the use of health services, (3) the impact of health programs on utilization patterns and on health status, and (4) the impact of therapeutic services on outcomes for specific diseases. Additional health services issues that are relevant to epidemiology are suggested. T h e application o f epidemiological m e t h o d s to health services research is not a new field o f e n d e a v o r , but the rationale for this application, as well as the similarities to research in the m o r e traditional epidemiological domains, has not frequently b e e n stressed. T h e usual epidemiological approaches---descriptive, analytic, a n d e x p e r i m e n t a l - - a r e all used in health services research and, in addition, m e t h o d s o f evaluation have b e e n e x p a n d e d t h r o u g h their application to p r o b l e m s in health services. T h e health services system m a y be envisioned as one o f the d e t e r m i n a n t s o f health a n d disease in m a n and, as such, it is equally as i m p o r t a n t to study the system itself f r o m an epidemiological perspective as it is to study e n v i r o n m e n t a l factors or circumstances o f life style. Modification in any o f these " d e t e r m i n a n t s o f disease" can have an i m p a c t on health. T h u s , the epidemiologist m a y a p p r o priately b r o a d e n his interests in health services b e y o n d those that relate strictly to the i m p a c t services have on the health o f a c o m m u n i t y or a subset o f the p o p u l a tion. Conceptualization o f the issues in health services should help to identify those that are m o s t a m e n a b l e to, a n d compatible with, epidemiological m e t h o d s . T h e scheme that follows is not i n t e n d e d to be a c o m p r e h e n s i v e view o f all health service issues, but r a t h e r an a t t e m p t to focus on those o f particular interest to epidemiologists. Certainly, an economist or a d m i n i s t r a t o r would outline a diff e r e n t series o f issues a n d a n o t h e r sequence o f relationships as well as utilize d i f f e r e n t r e s e a r c h strategies to answer his questions p e r t a i n i n g to these issues. C o n s i d e r that the d i a g r a m p r e s e n t e d in Figure 1 m a y a p p l y to m a n y d i f f e r e n t types o f target populations, r a n g i n g f r o m a total c o m m u n i t y to a subset
Dr. Hulka is Professor in the Department of Epidemiology at the School of Public Health, University of North Carolina, Chapel Hill, North Carolina 27514. This paper was prepared for presentation at the American Public Health Association Meeting in Miami, Florida, October 20, 1976. 140
0094-5145/78/1600-0140500.95 © 1978 H u m a n Sciences Press
Hulka
141
CONCEPTUALFRAMEWORKFOREPIDEMIOLOGICALAPPLICATIONSTO HEALTHSERVICESRESEARCH
Testor procedure defines risk level, diseasestatus
~._~a availability 3 accessibilityI-1 cceptability_]1 Need
Demand
DiseaseRiskHigh/~12
Use
Outcome
~
Target .~' Population
-
[_~ DiseaseRiskLow/ ~.F 5 Non-diseased I-- 6
Risk Levelor DiseaseStatus
.I
FIGURE 1: Conceptual Framework for Epidemiological Applications to Health Services Research Definition of Pathways: 1. Compliant. Use of services is appropriate in relation to need. 2. Non-Compliant. Use of services is incomplete. 3. Inaccessible. Demand is not realized in use of services. 4. Unmet needs. Services are not used in spite of a high level of need. 5. "Worried well". Services are used without apparent need. 6. Healthy. Absence of need results in no use of services. o f diseased persons. T h e latter would be stratified into various categories o f need, not by level o f risk o f disease but by a combination o f prognostic variables. In clinical epidemiology, a f r e q u e n t l y e n c o u n t e r e d target population would be a d e f i n e d g r o u p o f diseased persons for w h o m the effect o f a particular p r o c e d u r e or t h e r a p y is to be d e t e r m i n e d by the way in which it alters the natural history o f the disease. A few illustrations in applying the model may be useful: All adults in a defined c o m m u n i t y can be c o n s i d e r e d as the target population. Screening this population for elevated blood pressure would result in the identification o f a subset o f persons with suspected hypertension, a known risk factor for a variety of adverse health outcomes. Hypertensive persons would then be e n c o u r a g e d to use the health care system for diagnosis, treatment, and follow-up in o r d e r to r e d u c e their blood pressure levels and their concomitant liability to complications. However, as suggested by the model, the services must be accessible and acceptable to the potential user so that the a p p r o p r i a t e processes can be initiated and maintained. In the absence o f accessible or acceptable services, path 3 may be followed. I f the patient chooses to leave the system, he is labeled noncompliant; or if the p r o v i d e r terminates follow-up, rejection o f the patient has occurred. T h e s e options are d i a g r a m m e d as path 2. Such patients may then be subject to health outcomes m o r e similar to those o f hypertensive persons who never use the health care services (path 4). T h e g r o u p o f hypertensives who
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remain under care are considered compliant snd would be expected to achieve the most desirable health outcomes (path 1). The diagram also illustrates that, from a strictly medical standpoint, health services would not be indicated for normotensive individuals; path 6 shows their exclusion. However, because a portion of this group might still wish to use services for either confirmation or reassurance purposes, this is indicated by path 5. Sidney Garfield and his colleagues have labeled this latter group the "worried well"? Another example of the model's applicability might focus on a target population of persons with an existing diagnosed disease, for example, coronary heart disease. The estimate of need for services would now be based not on a determination of the degree of risk of disease but on the prognostic stratification of the patients, according to the severity of their disease; the tests or procedures used to define the severity levels would be biochemical and physiologic measurements and historical events. All patients would require services; none would appropriately follow the no-service pathways (paths 3, 4, and 6), but the complexity and intensity of services would be determined by the patient's prognostic classification. Because the capability of the health care system is limited in the extent that it can modify the course of the disease and to the extent that it may have differential effectiveness with different prognostic categories, the outcomes among patient categories would probably not be comparable. In these examples, selective factors exist that are largely responsible for the different pathways followed by the individuals who make up the target population. Because of these selective factors, some of which we can measure but few of which we can influence, direct comparisons of the outcomes experienced by the persons pursuing the various pathways are inappropriate. Only in the unusual situation, when the selective factors are understood and measurable, can they be controlled as confounding variables in an analysis. The ideal solution to the problems presented by selective factors is the use of an experimental research design. If the high risk or diseased subset of the target population can be randomly allocated into experimental and control groups, and if the latter group is not offered services or is assugned to its "usual source of care" whereas the experimental group has appropriate services readily available, the selective factors may be resolved, particularly if a very large proportion of the experimental group actually uses the services recommended, e.g., elects to take the compliant pathway (path 1). Although random allocation is desirable in terms of the research design, the ethical problems created by such a plan may be insurmountable. Whether or not random allocation is ethical depends on a number of factors, a few of which should be noted: the nature of the target population, whether it be a true population sample or a patient sample; the presumed efficacy of the service or therapy provided in comparison with none or usual treatment; and the character and severity of possible outcomes. In addition to the important ethical considerations, the political implications and the patient's personal willingness to participate in a randomized design are additional potential hindrances.
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The need for alternatives to randomization has increased the use of epidemiological methods for evaluation. A frequently used approach involves the selection of an additional population as a comparison group. The scientific adequacy of this method depends on the degree of comparability of the experimental and comparison groups on all the variables that are known to affect the outcomes under study. Because the comparison group will not receive the same services or the interventions that are reserved for the experimental group, circumstantial factors (such as limited funding, differences in political jurisdictions, or programmatic restrictions) may inadvertently create a setting in which this approach is both feasible and ethical. Various other quasi-experimental designs are being used and have been summarized by Campbell and Stanley.2 Next, let us consider examples of research that are consistent with the interests of epidemiologists and the conceptual framework presented. These topics include the need for health care, the use of services, the effect health services have on utilization patterns or on health status, and the effect therapeutic services have on disease outcomes. Within each of these areas, the research design chosen is often descriptive and incorporates methods adapted from the social sciences, as well as from epidemiology; other designs are analytical (hypothesis testing) or evaluative. Experimental designs, of which the clinical trial is a prime example, are abundantly represented in the epidemiological literature and, therefore, will not be emphasized in this brief review. N e e d for Health Care
The essence of epidemiology rests on the study of health and disease in population subsets. Traditionally, data on mortality and morbidity have been used to estimate health status and the need for services. Although mortality data in the United States are very reliable as a measure of the fact of death, and moderately reliable as to cause of death, morbidity data are still difficult to obtain on a consistent, nationwide basis. Problems of definition exist, depending on the source of data and the perspective of the respondent. Moreover, the frequency of any particular disease entity will vary as a function of the information source, whether it be death certificates, hospital discharge summaries, medical records from primary care physicians, or surveys of lay respondents. The definition of a disease or health problem will differ for the health professional as compared with the lay person. For these reasons, data on disease frequency are often inconsistent, and the classification schemes for illness and injury vary. To obtain population-based data, health interview surveys are used, of which the National Health Interview Survey is the best-known example. Data may be collected by interview, questionnaire, or diary methods, each of which is suitable for obtaining qualitatively and quantitatively different types of data. A survey using both the interview and diary methods was the Rochester Child Health Survey.a'4 This research sought to identify the health problems and illness behavior of families with children. The study focused on economically deprived families who might be expected to have an increased array of health
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and social problems, but with few resources to meet them (resources here being defined both in terms of personal means and also the availability of health care facilities). Although it was anticipated that the advent of Medicaid would increase the scope of available resources by reducing the cost barrier, and that increased utilization would in turn reduce the unm et health care needs, this effect was not demonstrated. 5 T h e earlier patterns of use persisted, both with respect to the volume and the source of care. Another study to identify unm e t health needs was undertaken among black adolescents ages 12 to 17 years in central Harlem in New York City.6 Youngsters were interviewed to identify their health problems as they themselves perceived them, with a follow-up physical examination conducted on 74% of those interviewed. Unlike previously reported studies, 7 a good concordance was found between the problems identified by respondent interview and the physical examination. Vision and respiratory problems were the ones most frequently identified by both methods. A full 50% of the 556 youngsters examined required referral for medical care. Participation in both the interview and physical examination decreased with increasing age, whereas the num ber of medical problems requiring referral increased with increasing age. T h e study revealed a high rate of u nm e t health needs and suggested that preventive efforts would be more effective if directed at younger, rather than older, adolescents. Assessments of health status and of need are essential to planning for health care resource allocation. Bloom and Peterson evaluated the prevalence of coronary care units in Massachusetts in relation to patient needs, s By using existing population-based data on the incidence of myocardial infarction and related serious cardiac disease, and assuming a travel time of no more than 30 minutes to a coronary care unit and a 95% probability of an available bed, the authors estimated the num be r of coronary care units and beds per unit that would be required to serve the population of the state. T h e estimates thus obtained indicated that the current n u m b e r of coronary care units could be halved, with a lesser reduction in the n u m b e r of beds; a cost saving of $3 million would ensue. Thus, the planning for medical services and resource allocation could be more effective if based on measures of disease frequency and other indices of health care needs. U s e o f Health Services
A classic study of the "natural history of medical care" was published in 1961 by White, Williams, and Greenberg. 9 Relying on data accumulated from a number o f sources in the United States and England, the authors developed a diagrammatic presentation of a hypothetical population of 1,000 persons, with their illness and health care utilization experiences over a one-month period. Among 1,000 adults (ages 16 years and over), about 750 will report an illness, of whom 250 will consult a physician. Among the 250, nine will be admitted to hospital, but only one of the nine will be hospitalized at a university medical
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center. Among the nine patients hospitalized, five will have been referred to another physician. The paradigm has clear implications for the education and training of physicians, most of which has been conducted, until recently, within the confines of the "Medical Center," where only the most selected group of patients with the most unrepresentative types of illness in relation to the population at large are ever seen. Certain subsets of utilization behavior are not completely realized in this model. For example, a portion of the visits for physician consultations are made by persons not reporting illness or injury during the month. Data from a household survey in one Midwestern city suggest that such visits account for about 9% of all medical consultations in a month2 ° Similarly, the subsets of patients referred to another physician may not be admitted to hospital. However, the overall approach clearly illustrates that persons tend to define their own illnesses (health care needs), after which they make a decision as to whether or not they should seek medical care (demand for services). If the decision to consult a physician is positive, the consultation may be followed by referral to another physician or hospitalization, or both (use of services). Effect o f H e a l t h P r o g r a m s and S e r v i c e s o n U t i l i z a t i o n Patterns
Because epidemiologists traditionally consider medical services or health care programs to be one of the determinants of illness and disease, one would like to be able to measure the effect services have on improving the health of the population served. The difficulties in achieving this goal are many; a few of the most intractable include: the long time span that is usually required before an effect can be expected to occur; the many factors external to the service provided that can affect the health of the target population; and the choice of an appropriate measure of health status. Because of the difficulties involved in a direct assessment of improved health status resulting from new programs or altered services, surrogate measures of program effectiveness are frequently employed; utilization patterns are a prime example. One example of this approach has already been mentioned: the potential impact of Medicaid (a financing mechanism) on the volume of services and the types of providers used by children from low-income families in Rochester, New York. ~ Very little change was demonstrated in this particular setting. Other studies have demonstrated changes in the use patterns that occurred after the introduction of new services or health facilities. The introduction of a neighborhood health center at Columbia Point in Boston had a marked effect on the number of hospital admissions and the length of hospital stay.11 The health center provided comprehensive ambulatory services to a low-income neighborhood (public housing project) that did not have access to most other medical services. By the end of the second full year of services, admissions to Boston City Hospital showed an 84% reduction compared with the admission rate during the 12 months prior to the opening of the center. The reduction
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JOURNAL OF COMMUNITY HEALTH
occurred on all major hospital services--medicine, obstetrics, and surgery--and could not be accounted for by increased admission rates by Columbia Point residents to other hospitals in the Boston area. Similar results using a different measure of changing utilization patterns were demonstrated in the Rochester area after the introduction of a neighborhood health center, a2 It was hypothesized that appropriate use of the center would result in a reduction in pediatric emergency department use. After two years of center operation, children in the center's catchment area had reduced their emergency department use by 38%. No reduction in pediatric emergency room visits was observed over the same time period by children outside of the center's catchment area, whereas suburban area children experienced a 29% increase in emergency room visits. Changes in overall population distribution, including the number of children in different georgraphic areas, were insufficient to account for the variation in emergency room use. The effect on utilization patterns of compulsory health insurance, which eliminated direct patient payment for medical care, was studied in the province of Quebec? Household surveys were conducted before and after insurance coverage was instituted in November 1970. A number of changes in use patterns were evident, with the most pronounced alterations occurring among lowincome persons. Although the average number of physician visits per person per year was not altered, the number increased for low-income persons and decreased for high-income persons. Low-income persons also experienced an increase in the percentage of potentially serious symptoms for which they sought medical care. Waiting to get an appointment with a physician and waiting time in the office prior to being seen both increased, with the largest increases in the higher-income groups. Compulsory health insurance with a reduction in outof-pocket costs (an accessibility factor) may have been responsible for the redistribution of the services used and the time required to obtain these services among the various subsets of the population. Effect of Health Service Programs on Community Health
Significant research in this area is not voluminous, for the reasons already mentioned. However, the two illustrations that follow were chosen specifically because they address important health issues and they exemplify two different methods useful in epidemiology. Any evaluative research strategy, using a comparison population demographically similar to the experimental population, was employed in a Baltimore study of rheumatic fever. The study was designed to examine the effectiveness of comprehensive care programs in preventing rheumatic fever/4 The impact of comprehensive care on the annual incidence of first hospitalized attacks of rheumatic fever among black children, aged 5 to 14 years, was compared for children from census tracts that were eligible for comprehensive care and similar children from three ineligible, but comparable, areas. Following the introduction of the program, the number of first hospitalizations was reduced by
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60% in the population eligible for comprehensive care. Those from the ineligible census tracts actually experienced an increase in the incidence of first hospitalizations for rheumatic fever over the same time period. These findings are particularly convincing because the extent of the reduction of first attacks was completely explained by a comparable reduction in prior clinical respiratory infections, the latter being amenable to medical therapy, e.g., treatment of streptococcal infection. The impact of screening activities on the stage of diagnosed disease, on the case-fatality rates, and, ultimately, on mortality is exemplified by the Health Insurance Plan of Greater New York randomized trial of breast cancer screening by clinical examination and mammography. 15"1~ Although one third of the women who were randomly allocated to the study group rejected screening, a number of important differences in outcome appeared between the study and control groups: A higher percentage of the women in the study group had no axillary node involvement at the time of diagnosis, as compared with the control group; the case-fatality rate was lower for the study group than for the controls at each stage of the disease; and mortality from breast cancer was reduced by about one third after five years of follow-up for the study women, compared with the controls. The differential in mortality occurred exclusively among women aged 50 years and over; no difference in mortality was found among women aged 40 to 49. These data support the concept that early diagnosis and intervention can favorably alter the natural history of breast cancer for some women with the disease. The use of an experimental research design lends additional credence to the validity of the findings. Effect of Therapeutic Services on Specific Diseases
Case-fatality for common surgical conditions is an important outcome, which can presumably be influenced by the quality of the service provided. Two papers addressed this topic, using routinely collected data from the General Register Office in England and Wales. aT'as For the three surgical conditions reviewed, a significant difference in the case-fatality rate was found in teaching versus non-teaching hospitals. Additional analyses on hyperplasia of the prostate, utilizing improved sampling methods for cases and hospital records from groups of teaching and regional-board hospitals, suggested factors pertaining to both patient selection and hospital performance that could account for the differences in patient outcomes. ~9 The most striking difference was in the percentage of "emergency" admissions to regional-board hospitals, compared with teaching hospitals: 78% and 22%, respectively. However, among the emergency admissions, the operative rate was low in regional-board hospitals with a high case-fatality (14%), whereas in teaching hospitals almost all emergency admissions received surgery and case-fatality was low (4.3%). Regional-Board hospitals appeared to have a poorer experience with their patients, both because of the admission of poorer risk patients and also because of the lesser resources and
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personnel allocated to them. The information obtained from this descriptive study formed the basis for recommendations to modify the service system. Another therapeutic intervention, which has been evaluated with less than the desired degree of epidemiological rigor, is the coronary care unit. As coronary care units are a relatively recent innovation in medical care, the opportunity existed at the time of their introduction to evaluate their effectiveness in a scientific and ethical fashion. Currently, the issue is more complicated, because coronary care units have become part of the customary and expected facilities at hospitals, both large and small; and health care providers, hospital board members, and the public at large have become convinced of their effectiveness. As a matter of scientific interest, very little is known about their effect on patient outcomes. One frequently quoted effort at a clinical trial was undertaken in southwest England. 2° The outcome of interest was the 28-day mortality rate for post-myocardial infarction patients. Of 1,203 episodes of infarction, only 343 (28%) of the cases were suitable for random allocation to hospital (coronary care unit) or home. The other cases were selected initially for hospital (or occasionally home care) by either the physician or the patient. Among those randomly allocated to hospital or home, the major prognostic risk factors were fairly equally distributed between the two groups, both of which experienced a similar 28-day mortality. Although generalization from this one experience would be unwise, the results hardly support the uncritical acceptance of this costly treatment modality for all myocardial infarction patients. Summary I have presented a model to illustrate the areas in which epidemiological thinking may be applied to health services research. The model is neither exhaustive nor exclusive, in that, other areas not specifically incorporated within the model lie within the domain of epidemiology, and several aspects of the model are also shared with researchers in other disciplines. Examples of epidemiological applications have been presented in the areas of the need for health care, the use of health services, the effect of health programs on utilization patterns or health status, and the effect of therapeutic services on the outcomes for specific diseases. Several omissions should be noted: Nothing was mentioned concerning studies on the process of care; that is, what actually goes on within the health care setting and what specific aspects of the process have an effect on the patient's outcome. Reference was made to the effects of specific health services in altering the natural history of disease only through the example of a screening program for breast cancer. Knowledge of the natural history of various diseases has been increased by the planned introduction of preventive or therapeutic services.2a'22 Lastly, clinical trials and community intervention studies that are major issues of the day, both in terms of their potential impact on public health and medical practice and also in terms of their commitment of resources, were largely ignored. This decision was made in order to pursue selectively less tra-
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d i t i o n a l t o p i c s in t h e r e a l m o f e p i d e m i o l o g i c a l a p p l i c a t i o n s to h e a l t h s e r v i c e s r e search.
REFERENCES 1. Garfield SR, Collen MF, Feldman R, et al: Evaluation of an ambulatory medical-care delivery system. N EnglJ Med 294:426-431, 1976. 2. Campbell DT, Stanley JC: Experimental and Quasi-ExperimentalDesignsfor Research. Chicago, Rand McNally College Publishing Co, 1963. Pp 34-64. 3. Roghmann KJ, Haggerty RJ: Rochester child health surveys I: Objectives, organization, and methods. Med Care 8:47-59, 1970. 4. Roghmann KJ, Haggerty RF: The diary as a research instrument in the study of health and illness behavior: Experiences with a random sample in young families. Med Care 10:143-163, 1972. 5. Roghmann KJ, Haggerty RJ, Lorenz R: Anticipated and actual effects of Medicaid on the medical-care pattern of children. N EnglJ Med 285:1053-1057, 1971. 6. Brunswick, AF, Josephson E: Adolescent health in Harlem. AmJ Public Health [Suppl] October 1972. Pp 147. 7. Elinson J, Trussell RE: Some factors relating to degree of correspondence for diagnostic information as obtained by household interviews and clinical examinations. Am J Public Health 47:311-321, 1957. 8. Bloom BS, Peterson IL: Patient needs and medical-care planning. N EnglJ Med 290:1171-1177, 1974. 9. White KL, Williams TF, Greenberg BG: The ecology of medical care. N EnglJ Med 265:885-892, 1961. 10. Daly M, Hulka BS: Ambulatory care in one community: Patient, provider, and visit characteristics.J Community Health 3:44-53, 1977. 11. Bellin SS, Geiger HJ, Gibson CD: Impact of ambulatory health-care services on the demand for hospital beds. N EnglJ Med 280:808-812, 1969. 12. Hochheiser LI, Woodward K, Charney E: Effect of the neighborhood health center on the use of pediatric emergency departments in Rochester, New York. N EnglJ Med 285:148-152, 1971. 13. Enterline PE, Salter V, McDonald AD, et al: The distribution of medical services before and after "free medical care--The Quebec experience. N EnglJ Med 289:1174-1178, 1973. 14. Gordis L: Effectiveness of comprehensive-care programs in preventing rheumatic fever. N Engl J Med 289:331-335, 1973. 15. Shapiro S. Strax P. Venet L: Periodic breast cancer screening in reducing mortality from breast cancer.JAMA 215: 1777-1785, 1971. 16. Shapiro S. Strax L. Venet W: Changes in 5-year breast cancer mortality in breast cancer screening program. 7th National Cancer Conference Proc 7: 663-678, 1973. 17. Lee JA, Morrison SL, Morris JN: Fatality from three common surgical conditions in teaching and non-teaching hospitals. Lancet 213: 785-790, 1957. 18. Lipworth L, Lee JA, Morris JN: Case-fatality in teaching and nonteaching hospitals, 1956-59. Med Care 1:71-76, 1963. 19. Ashley JSA, Howlett A, Morris JN: Case-fatality of hyperplasia of the prostate in two teaching and three regional-board hospitals. Lancet II: 1308-1311, 1971. 20. Mather HG, Pearson NG, Read KLQ, et al: Acute myocardial infarction: Home and hospital treatment. Br MedJ 3:334-338, 1971. 21. Hakama M, Rasanen-Virtanen U: Effect of a mass screening program on the risk of cervical cancer. Am J Epidemiol103: 512-517, 1976. 22. Shapiro S, Goldberg JD, Hutchinson GB: Lead Time in Breast Cancer Detection and Implications for Periodicity of Screening. AmJ Epidemiol 100:357-366, 1974.
EPIDEMIOLOGICAL
APPLICATIONS SERVICES
TO
HEALTH
RESEARCH
B a r b a r a S. Hulka, M.D., M.P.H.
ABSTRACT: A model is presented to illustrate some areas in which epidemiological thinking may be applied to health services research. The model is neither exhaustive nor exclusive, for other areas not specifically described as within the model are also a part of the domain of epidemiology, and several aspects of the model are shared with researchers in other disciplines. Selected examples of epidemiological applications are reviewed; these include: (1) the need for health care services, (2) the use of health services, (3) the impact of health programs on utilization patterns and on health status, and (4) the impact of therapeutic services on outcomes for specific diseases. Additional health services issues that are relevant to epidemiology are suggested. T h e application o f epidemiological m e t h o d s to health services research is not a new field o f e n d e a v o r , but the rationale for this application, as well as the similarities to research in the m o r e traditional epidemiological domains, has not frequently b e e n stressed. T h e usual epidemiological approaches---descriptive, analytic, a n d e x p e r i m e n t a l - - a r e all used in health services research and, in addition, m e t h o d s o f evaluation have b e e n e x p a n d e d t h r o u g h their application to p r o b l e m s in health services. T h e health services system m a y be envisioned as one o f the d e t e r m i n a n t s o f health a n d disease in m a n and, as such, it is equally as i m p o r t a n t to study the system itself f r o m an epidemiological perspective as it is to study e n v i r o n m e n t a l factors or circumstances o f life style. Modification in any o f these " d e t e r m i n a n t s o f disease" can have an i m p a c t on health. T h u s , the epidemiologist m a y a p p r o priately b r o a d e n his interests in health services b e y o n d those that relate strictly to the i m p a c t services have on the health o f a c o m m u n i t y or a subset o f the p o p u l a tion. Conceptualization o f the issues in health services should help to identify those that are m o s t a m e n a b l e to, a n d compatible with, epidemiological m e t h o d s . T h e scheme that follows is not i n t e n d e d to be a c o m p r e h e n s i v e view o f all health service issues, but r a t h e r an a t t e m p t to focus on those o f particular interest to epidemiologists. Certainly, an economist or a d m i n i s t r a t o r would outline a diff e r e n t series o f issues a n d a n o t h e r sequence o f relationships as well as utilize d i f f e r e n t r e s e a r c h strategies to answer his questions p e r t a i n i n g to these issues. C o n s i d e r that the d i a g r a m p r e s e n t e d in Figure 1 m a y a p p l y to m a n y d i f f e r e n t types o f target populations, r a n g i n g f r o m a total c o m m u n i t y to a subset
Dr. Hulka is Professor in the Department of Epidemiology at the School of Public Health, University of North Carolina, Chapel Hill, North Carolina 27514. This paper was prepared for presentation at the American Public Health Association Meeting in Miami, Florida, October 20, 1976. 140
0094-5145/78/1600-0140500.95 © 1978 H u m a n Sciences Press
Hulka
141
CONCEPTUALFRAMEWORKFOREPIDEMIOLOGICALAPPLICATIONSTO HEALTHSERVICESRESEARCH
Testor procedure defines risk level, diseasestatus
~._~a availability 3 accessibilityI-1 cceptability_]1 Need
Demand
DiseaseRiskHigh/~12
Use
Outcome
~
Target .~' Population
-
[_~ DiseaseRiskLow/ ~.F 5 Non-diseased I-- 6
Risk Levelor DiseaseStatus
.I
FIGURE 1: Conceptual Framework for Epidemiological Applications to Health Services Research Definition of Pathways: 1. Compliant. Use of services is appropriate in relation to need. 2. Non-Compliant. Use of services is incomplete. 3. Inaccessible. Demand is not realized in use of services. 4. Unmet needs. Services are not used in spite of a high level of need. 5. "Worried well". Services are used without apparent need. 6. Healthy. Absence of need results in no use of services. o f diseased persons. T h e latter would be stratified into various categories o f need, not by level o f risk o f disease but by a combination o f prognostic variables. In clinical epidemiology, a f r e q u e n t l y e n c o u n t e r e d target population would be a d e f i n e d g r o u p o f diseased persons for w h o m the effect o f a particular p r o c e d u r e or t h e r a p y is to be d e t e r m i n e d by the way in which it alters the natural history o f the disease. A few illustrations in applying the model may be useful: All adults in a defined c o m m u n i t y can be c o n s i d e r e d as the target population. Screening this population for elevated blood pressure would result in the identification o f a subset o f persons with suspected hypertension, a known risk factor for a variety of adverse health outcomes. Hypertensive persons would then be e n c o u r a g e d to use the health care system for diagnosis, treatment, and follow-up in o r d e r to r e d u c e their blood pressure levels and their concomitant liability to complications. However, as suggested by the model, the services must be accessible and acceptable to the potential user so that the a p p r o p r i a t e processes can be initiated and maintained. In the absence o f accessible or acceptable services, path 3 may be followed. I f the patient chooses to leave the system, he is labeled noncompliant; or if the p r o v i d e r terminates follow-up, rejection o f the patient has occurred. T h e s e options are d i a g r a m m e d as path 2. Such patients may then be subject to health outcomes m o r e similar to those o f hypertensive persons who never use the health care services (path 4). T h e g r o u p o f hypertensives who
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remain under care are considered compliant snd would be expected to achieve the most desirable health outcomes (path 1). The diagram also illustrates that, from a strictly medical standpoint, health services would not be indicated for normotensive individuals; path 6 shows their exclusion. However, because a portion of this group might still wish to use services for either confirmation or reassurance purposes, this is indicated by path 5. Sidney Garfield and his colleagues have labeled this latter group the "worried well"? Another example of the model's applicability might focus on a target population of persons with an existing diagnosed disease, for example, coronary heart disease. The estimate of need for services would now be based not on a determination of the degree of risk of disease but on the prognostic stratification of the patients, according to the severity of their disease; the tests or procedures used to define the severity levels would be biochemical and physiologic measurements and historical events. All patients would require services; none would appropriately follow the no-service pathways (paths 3, 4, and 6), but the complexity and intensity of services would be determined by the patient's prognostic classification. Because the capability of the health care system is limited in the extent that it can modify the course of the disease and to the extent that it may have differential effectiveness with different prognostic categories, the outcomes among patient categories would probably not be comparable. In these examples, selective factors exist that are largely responsible for the different pathways followed by the individuals who make up the target population. Because of these selective factors, some of which we can measure but few of which we can influence, direct comparisons of the outcomes experienced by the persons pursuing the various pathways are inappropriate. Only in the unusual situation, when the selective factors are understood and measurable, can they be controlled as confounding variables in an analysis. The ideal solution to the problems presented by selective factors is the use of an experimental research design. If the high risk or diseased subset of the target population can be randomly allocated into experimental and control groups, and if the latter group is not offered services or is assugned to its "usual source of care" whereas the experimental group has appropriate services readily available, the selective factors may be resolved, particularly if a very large proportion of the experimental group actually uses the services recommended, e.g., elects to take the compliant pathway (path 1). Although random allocation is desirable in terms of the research design, the ethical problems created by such a plan may be insurmountable. Whether or not random allocation is ethical depends on a number of factors, a few of which should be noted: the nature of the target population, whether it be a true population sample or a patient sample; the presumed efficacy of the service or therapy provided in comparison with none or usual treatment; and the character and severity of possible outcomes. In addition to the important ethical considerations, the political implications and the patient's personal willingness to participate in a randomized design are additional potential hindrances.
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The need for alternatives to randomization has increased the use of epidemiological methods for evaluation. A frequently used approach involves the selection of an additional population as a comparison group. The scientific adequacy of this method depends on the degree of comparability of the experimental and comparison groups on all the variables that are known to affect the outcomes under study. Because the comparison group will not receive the same services or the interventions that are reserved for the experimental group, circumstantial factors (such as limited funding, differences in political jurisdictions, or programmatic restrictions) may inadvertently create a setting in which this approach is both feasible and ethical. Various other quasi-experimental designs are being used and have been summarized by Campbell and Stanley.2 Next, let us consider examples of research that are consistent with the interests of epidemiologists and the conceptual framework presented. These topics include the need for health care, the use of services, the effect health services have on utilization patterns or on health status, and the effect therapeutic services have on disease outcomes. Within each of these areas, the research design chosen is often descriptive and incorporates methods adapted from the social sciences, as well as from epidemiology; other designs are analytical (hypothesis testing) or evaluative. Experimental designs, of which the clinical trial is a prime example, are abundantly represented in the epidemiological literature and, therefore, will not be emphasized in this brief review. N e e d for Health Care
The essence of epidemiology rests on the study of health and disease in population subsets. Traditionally, data on mortality and morbidity have been used to estimate health status and the need for services. Although mortality data in the United States are very reliable as a measure of the fact of death, and moderately reliable as to cause of death, morbidity data are still difficult to obtain on a consistent, nationwide basis. Problems of definition exist, depending on the source of data and the perspective of the respondent. Moreover, the frequency of any particular disease entity will vary as a function of the information source, whether it be death certificates, hospital discharge summaries, medical records from primary care physicians, or surveys of lay respondents. The definition of a disease or health problem will differ for the health professional as compared with the lay person. For these reasons, data on disease frequency are often inconsistent, and the classification schemes for illness and injury vary. To obtain population-based data, health interview surveys are used, of which the National Health Interview Survey is the best-known example. Data may be collected by interview, questionnaire, or diary methods, each of which is suitable for obtaining qualitatively and quantitatively different types of data. A survey using both the interview and diary methods was the Rochester Child Health Survey.a'4 This research sought to identify the health problems and illness behavior of families with children. The study focused on economically deprived families who might be expected to have an increased array of health
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and social problems, but with few resources to meet them (resources here being defined both in terms of personal means and also the availability of health care facilities). Although it was anticipated that the advent of Medicaid would increase the scope of available resources by reducing the cost barrier, and that increased utilization would in turn reduce the unm et health care needs, this effect was not demonstrated. 5 T h e earlier patterns of use persisted, both with respect to the volume and the source of care. Another study to identify unm e t health needs was undertaken among black adolescents ages 12 to 17 years in central Harlem in New York City.6 Youngsters were interviewed to identify their health problems as they themselves perceived them, with a follow-up physical examination conducted on 74% of those interviewed. Unlike previously reported studies, 7 a good concordance was found between the problems identified by respondent interview and the physical examination. Vision and respiratory problems were the ones most frequently identified by both methods. A full 50% of the 556 youngsters examined required referral for medical care. Participation in both the interview and physical examination decreased with increasing age, whereas the num ber of medical problems requiring referral increased with increasing age. T h e study revealed a high rate of u nm e t health needs and suggested that preventive efforts would be more effective if directed at younger, rather than older, adolescents. Assessments of health status and of need are essential to planning for health care resource allocation. Bloom and Peterson evaluated the prevalence of coronary care units in Massachusetts in relation to patient needs, s By using existing population-based data on the incidence of myocardial infarction and related serious cardiac disease, and assuming a travel time of no more than 30 minutes to a coronary care unit and a 95% probability of an available bed, the authors estimated the num be r of coronary care units and beds per unit that would be required to serve the population of the state. T h e estimates thus obtained indicated that the current n u m b e r of coronary care units could be halved, with a lesser reduction in the n u m b e r of beds; a cost saving of $3 million would ensue. Thus, the planning for medical services and resource allocation could be more effective if based on measures of disease frequency and other indices of health care needs. U s e o f Health Services
A classic study of the "natural history of medical care" was published in 1961 by White, Williams, and Greenberg. 9 Relying on data accumulated from a number o f sources in the United States and England, the authors developed a diagrammatic presentation of a hypothetical population of 1,000 persons, with their illness and health care utilization experiences over a one-month period. Among 1,000 adults (ages 16 years and over), about 750 will report an illness, of whom 250 will consult a physician. Among the 250, nine will be admitted to hospital, but only one of the nine will be hospitalized at a university medical
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center. Among the nine patients hospitalized, five will have been referred to another physician. The paradigm has clear implications for the education and training of physicians, most of which has been conducted, until recently, within the confines of the "Medical Center," where only the most selected group of patients with the most unrepresentative types of illness in relation to the population at large are ever seen. Certain subsets of utilization behavior are not completely realized in this model. For example, a portion of the visits for physician consultations are made by persons not reporting illness or injury during the month. Data from a household survey in one Midwestern city suggest that such visits account for about 9% of all medical consultations in a month2 ° Similarly, the subsets of patients referred to another physician may not be admitted to hospital. However, the overall approach clearly illustrates that persons tend to define their own illnesses (health care needs), after which they make a decision as to whether or not they should seek medical care (demand for services). If the decision to consult a physician is positive, the consultation may be followed by referral to another physician or hospitalization, or both (use of services). Effect o f H e a l t h P r o g r a m s and S e r v i c e s o n U t i l i z a t i o n Patterns
Because epidemiologists traditionally consider medical services or health care programs to be one of the determinants of illness and disease, one would like to be able to measure the effect services have on improving the health of the population served. The difficulties in achieving this goal are many; a few of the most intractable include: the long time span that is usually required before an effect can be expected to occur; the many factors external to the service provided that can affect the health of the target population; and the choice of an appropriate measure of health status. Because of the difficulties involved in a direct assessment of improved health status resulting from new programs or altered services, surrogate measures of program effectiveness are frequently employed; utilization patterns are a prime example. One example of this approach has already been mentioned: the potential impact of Medicaid (a financing mechanism) on the volume of services and the types of providers used by children from low-income families in Rochester, New York. ~ Very little change was demonstrated in this particular setting. Other studies have demonstrated changes in the use patterns that occurred after the introduction of new services or health facilities. The introduction of a neighborhood health center at Columbia Point in Boston had a marked effect on the number of hospital admissions and the length of hospital stay.11 The health center provided comprehensive ambulatory services to a low-income neighborhood (public housing project) that did not have access to most other medical services. By the end of the second full year of services, admissions to Boston City Hospital showed an 84% reduction compared with the admission rate during the 12 months prior to the opening of the center. The reduction
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occurred on all major hospital services--medicine, obstetrics, and surgery--and could not be accounted for by increased admission rates by Columbia Point residents to other hospitals in the Boston area. Similar results using a different measure of changing utilization patterns were demonstrated in the Rochester area after the introduction of a neighborhood health center, a2 It was hypothesized that appropriate use of the center would result in a reduction in pediatric emergency department use. After two years of center operation, children in the center's catchment area had reduced their emergency department use by 38%. No reduction in pediatric emergency room visits was observed over the same time period by children outside of the center's catchment area, whereas suburban area children experienced a 29% increase in emergency room visits. Changes in overall population distribution, including the number of children in different georgraphic areas, were insufficient to account for the variation in emergency room use. The effect on utilization patterns of compulsory health insurance, which eliminated direct patient payment for medical care, was studied in the province of Quebec? Household surveys were conducted before and after insurance coverage was instituted in November 1970. A number of changes in use patterns were evident, with the most pronounced alterations occurring among lowincome persons. Although the average number of physician visits per person per year was not altered, the number increased for low-income persons and decreased for high-income persons. Low-income persons also experienced an increase in the percentage of potentially serious symptoms for which they sought medical care. Waiting to get an appointment with a physician and waiting time in the office prior to being seen both increased, with the largest increases in the higher-income groups. Compulsory health insurance with a reduction in outof-pocket costs (an accessibility factor) may have been responsible for the redistribution of the services used and the time required to obtain these services among the various subsets of the population. Effect of Health Service Programs on Community Health
Significant research in this area is not voluminous, for the reasons already mentioned. However, the two illustrations that follow were chosen specifically because they address important health issues and they exemplify two different methods useful in epidemiology. Any evaluative research strategy, using a comparison population demographically similar to the experimental population, was employed in a Baltimore study of rheumatic fever. The study was designed to examine the effectiveness of comprehensive care programs in preventing rheumatic fever/4 The impact of comprehensive care on the annual incidence of first hospitalized attacks of rheumatic fever among black children, aged 5 to 14 years, was compared for children from census tracts that were eligible for comprehensive care and similar children from three ineligible, but comparable, areas. Following the introduction of the program, the number of first hospitalizations was reduced by
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60% in the population eligible for comprehensive care. Those from the ineligible census tracts actually experienced an increase in the incidence of first hospitalizations for rheumatic fever over the same time period. These findings are particularly convincing because the extent of the reduction of first attacks was completely explained by a comparable reduction in prior clinical respiratory infections, the latter being amenable to medical therapy, e.g., treatment of streptococcal infection. The impact of screening activities on the stage of diagnosed disease, on the case-fatality rates, and, ultimately, on mortality is exemplified by the Health Insurance Plan of Greater New York randomized trial of breast cancer screening by clinical examination and mammography. 15"1~ Although one third of the women who were randomly allocated to the study group rejected screening, a number of important differences in outcome appeared between the study and control groups: A higher percentage of the women in the study group had no axillary node involvement at the time of diagnosis, as compared with the control group; the case-fatality rate was lower for the study group than for the controls at each stage of the disease; and mortality from breast cancer was reduced by about one third after five years of follow-up for the study women, compared with the controls. The differential in mortality occurred exclusively among women aged 50 years and over; no difference in mortality was found among women aged 40 to 49. These data support the concept that early diagnosis and intervention can favorably alter the natural history of breast cancer for some women with the disease. The use of an experimental research design lends additional credence to the validity of the findings. Effect of Therapeutic Services on Specific Diseases
Case-fatality for common surgical conditions is an important outcome, which can presumably be influenced by the quality of the service provided. Two papers addressed this topic, using routinely collected data from the General Register Office in England and Wales. aT'as For the three surgical conditions reviewed, a significant difference in the case-fatality rate was found in teaching versus non-teaching hospitals. Additional analyses on hyperplasia of the prostate, utilizing improved sampling methods for cases and hospital records from groups of teaching and regional-board hospitals, suggested factors pertaining to both patient selection and hospital performance that could account for the differences in patient outcomes. ~9 The most striking difference was in the percentage of "emergency" admissions to regional-board hospitals, compared with teaching hospitals: 78% and 22%, respectively. However, among the emergency admissions, the operative rate was low in regional-board hospitals with a high case-fatality (14%), whereas in teaching hospitals almost all emergency admissions received surgery and case-fatality was low (4.3%). Regional-Board hospitals appeared to have a poorer experience with their patients, both because of the admission of poorer risk patients and also because of the lesser resources and
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personnel allocated to them. The information obtained from this descriptive study formed the basis for recommendations to modify the service system. Another therapeutic intervention, which has been evaluated with less than the desired degree of epidemiological rigor, is the coronary care unit. As coronary care units are a relatively recent innovation in medical care, the opportunity existed at the time of their introduction to evaluate their effectiveness in a scientific and ethical fashion. Currently, the issue is more complicated, because coronary care units have become part of the customary and expected facilities at hospitals, both large and small; and health care providers, hospital board members, and the public at large have become convinced of their effectiveness. As a matter of scientific interest, very little is known about their effect on patient outcomes. One frequently quoted effort at a clinical trial was undertaken in southwest England. 2° The outcome of interest was the 28-day mortality rate for post-myocardial infarction patients. Of 1,203 episodes of infarction, only 343 (28%) of the cases were suitable for random allocation to hospital (coronary care unit) or home. The other cases were selected initially for hospital (or occasionally home care) by either the physician or the patient. Among those randomly allocated to hospital or home, the major prognostic risk factors were fairly equally distributed between the two groups, both of which experienced a similar 28-day mortality. Although generalization from this one experience would be unwise, the results hardly support the uncritical acceptance of this costly treatment modality for all myocardial infarction patients. Summary I have presented a model to illustrate the areas in which epidemiological thinking may be applied to health services research. The model is neither exhaustive nor exclusive, in that, other areas not specifically incorporated within the model lie within the domain of epidemiology, and several aspects of the model are also shared with researchers in other disciplines. Examples of epidemiological applications have been presented in the areas of the need for health care, the use of health services, the effect of health programs on utilization patterns or health status, and the effect of therapeutic services on the outcomes for specific diseases. Several omissions should be noted: Nothing was mentioned concerning studies on the process of care; that is, what actually goes on within the health care setting and what specific aspects of the process have an effect on the patient's outcome. Reference was made to the effects of specific health services in altering the natural history of disease only through the example of a screening program for breast cancer. Knowledge of the natural history of various diseases has been increased by the planned introduction of preventive or therapeutic services.2a'22 Lastly, clinical trials and community intervention studies that are major issues of the day, both in terms of their potential impact on public health and medical practice and also in terms of their commitment of resources, were largely ignored. This decision was made in order to pursue selectively less tra-
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d i t i o n a l t o p i c s in t h e r e a l m o f e p i d e m i o l o g i c a l a p p l i c a t i o n s to h e a l t h s e r v i c e s r e search.
REFERENCES 1. Garfield SR, Collen MF, Feldman R, et al: Evaluation of an ambulatory medical-care delivery system. N EnglJ Med 294:426-431, 1976. 2. Campbell DT, Stanley JC: Experimental and Quasi-ExperimentalDesignsfor Research. Chicago, Rand McNally College Publishing Co, 1963. Pp 34-64. 3. Roghmann KJ, Haggerty RJ: Rochester child health surveys I: Objectives, organization, and methods. Med Care 8:47-59, 1970. 4. Roghmann KJ, Haggerty RF: The diary as a research instrument in the study of health and illness behavior: Experiences with a random sample in young families. Med Care 10:143-163, 1972. 5. Roghmann KJ, Haggerty RJ, Lorenz R: Anticipated and actual effects of Medicaid on the medical-care pattern of children. N EnglJ Med 285:1053-1057, 1971. 6. Brunswick, AF, Josephson E: Adolescent health in Harlem. AmJ Public Health [Suppl] October 1972. Pp 147. 7. Elinson J, Trussell RE: Some factors relating to degree of correspondence for diagnostic information as obtained by household interviews and clinical examinations. Am J Public Health 47:311-321, 1957. 8. Bloom BS, Peterson IL: Patient needs and medical-care planning. N EnglJ Med 290:1171-1177, 1974. 9. White KL, Williams TF, Greenberg BG: The ecology of medical care. N EnglJ Med 265:885-892, 1961. 10. Daly M, Hulka BS: Ambulatory care in one community: Patient, provider, and visit characteristics.J Community Health 3:44-53, 1977. 11. Bellin SS, Geiger HJ, Gibson CD: Impact of ambulatory health-care services on the demand for hospital beds. N EnglJ Med 280:808-812, 1969. 12. Hochheiser LI, Woodward K, Charney E: Effect of the neighborhood health center on the use of pediatric emergency departments in Rochester, New York. N EnglJ Med 285:148-152, 1971. 13. Enterline PE, Salter V, McDonald AD, et al: The distribution of medical services before and after "free medical care--The Quebec experience. N EnglJ Med 289:1174-1178, 1973. 14. Gordis L: Effectiveness of comprehensive-care programs in preventing rheumatic fever. N Engl J Med 289:331-335, 1973. 15. Shapiro S. Strax P. Venet L: Periodic breast cancer screening in reducing mortality from breast cancer.JAMA 215: 1777-1785, 1971. 16. Shapiro S. Strax L. Venet W: Changes in 5-year breast cancer mortality in breast cancer screening program. 7th National Cancer Conference Proc 7: 663-678, 1973. 17. Lee JA, Morrison SL, Morris JN: Fatality from three common surgical conditions in teaching and non-teaching hospitals. Lancet 213: 785-790, 1957. 18. Lipworth L, Lee JA, Morris JN: Case-fatality in teaching and nonteaching hospitals, 1956-59. Med Care 1:71-76, 1963. 19. Ashley JSA, Howlett A, Morris JN: Case-fatality of hyperplasia of the prostate in two teaching and three regional-board hospitals. Lancet II: 1308-1311, 1971. 20. Mather HG, Pearson NG, Read KLQ, et al: Acute myocardial infarction: Home and hospital treatment. Br MedJ 3:334-338, 1971. 21. Hakama M, Rasanen-Virtanen U: Effect of a mass screening program on the risk of cervical cancer. Am J Epidemiol103: 512-517, 1976. 22. Shapiro S, Goldberg JD, Hutchinson GB: Lead Time in Breast Cancer Detection and Implications for Periodicity of Screening. AmJ Epidemiol 100:357-366, 1974.
