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Implications of epidemiology for community medicine
PREVENTIVE
12, 150- 154 (1983)
MEDICINE
Implications
of Epidemiology THOMAS
World Health
Organization,
for Community
Medicine’
STRASSER CH-1211 Geneva 27, Switzerland
Although both epidemiology and community medicine are difftcult to define, the relationship between them can be described in practical terms. Examples are given in which cardiovascular epidemiological studies demonstrated the need (a) for improving existing community health care services, (b) for extending them, (c) for transposing them to new settings, (d) for starting preventive measures early in life, and (e) for inducing population-wide changes. However, community medicine has many limitations, calling for a better information base, and also calling for more epidemiological research.
EPIDEMIOLOGY
AND COMMUNITY
MEDICINE
Epidemiology has been called “the basic science of community medicine” (7). Conversely, community medicine has been regarded as “the practice arm of epidemiology” (1). Thus it is seemingly easy to describe the relationship between epidemiology and community medicine despite the difficulties of defining epidemiology itself (6) and despite the fact that “sociologists and others have already expended a great deal of effort in trying to define community without reaching any appreciable degree of consensus” (20). I shall try to describe this relationship, using examples of cardiovascular prevention studies in which I have personal experience. THE NEED FOR IMPROVING EXISTING COMMUNITY HEALTH CARE: DELAYS OCCURRING BEFORE REACHING MEDICAL CARE FOR ACUTE MYOCARDIAL INFARCTION
In a study of incidence of acute myocardial infarction (19), an analysis was made of the time elapsed from the onset of symptoms to various events in health care. Figure 1 shows, for selected communities, the median times between the beginning of the attack and the call for medical help, the first examination, and hospital admission. These times, very different in various communities, are indicative of the efficiency of emergency care for patients with acute myocardial infarctionand show which links in the health care chain were the weakest at the time of the study. It can be concluded in one case that the education of the public need be reinforced; in another, that the ambulance services need revision; and in a third case, physician responsiveness in this community needs improvement as well. THE NEED FOR EXTENDING COMMUNITY HEALTH CARE: HYPERTENSION COMMUNITY CONTROL PROGRAMS
In the late 1960s and early 1970s a number of surveys in various parts of the world established the fact, surprising to clinicians, that blood pressure was indeed ’ Presented at the International Symposium Disease, June 24-26, 1981, Anacapri, Italy.
on Epidemiology
150 0091.7435/83/010150-05$03.00/O Copyright All rights
@ 1983 by Academic Press, Inc. of reproduction in any form reserved.
and Prevention
of Atherosclerotic
SYMPOSIUM:
ATHEROSCLEROTIC
DISEASE
151
GO Ta so He L" Bu Be
0
100
200
300
400
500 min.
FIG. 1. Median time elapsed since onset of heart attack in seven European communities. There are considerable dilferences between the structures of hospital admission delay. Go is Goteborg, Sweden; Ta is Tampere, Finland; Bo is Boden, Sweden: He is Helsinki, Finland; Lu is Lublin, Poland: Bu is Bucharest, Romania; Be is Berlin, German Democratic Republic.
under control in only a small fraction of hypertensive subjects. Since the positive effect of hypertension treatment had been demonstrated, the obvious conclusion was that health care needed to be extended to all hypertensives in the community, and hypertension community control programs such as the WHO Cooperative Project (2) or the U.S. National High Blood Pressure Education Program (8) were instituted. Such programs have, indeed, reduced the proportion of untreated and undiagnosed hypertensives in the project communities. TRANSPOSING SETTINGS:
ESTABLISHED PREVENTIVE MEASURES TO NEW RHEUMATIC FEVER PREVENTION PROGRAMS IN DEVELOPING COUNTRIES
The effectiveness of penicillin prevention of rheumatic fever recurrences became evident in a number of community studies in the U.S. soon after the advent of penicillin. In the 1960s it also became increasingly obvious that rheumatic fever, by this time tending to disappear from affluent countries (although persisting in Western slums), was an important public health problem in developing countries. It had to be assessed whether the prevention of rheumatic heart disease in those developing, mainly tropical and subtropical, countries indeed required community control programs, and whether these were feasible and justified as well. A multicenter cooperative community project coordinated by WHO in nine developing countries (3) has shown that the cost of penicillin dispensed for prevention was amply discounted by the hospital days averted. All other benefits presented a net gain (15). THE NEED FOR AN EARLY START: ATHEROSCLEROSIS AND ITS PREVENTION IN YOUTH
A population-based anatomical study in five European towns, organized by WHO in the late 1960s (IO), confirmed that coronary atherosclerosis is considerably more prevalent than clinically manifest ischemic heart disease. A finding of capital importance was that the process started early: some 10% of boys and girls aged 10 to 14 already had raised atherosclerotic lesions in the coronary arteries-a
152
THOMAS
STRASSER
finding that forcefully emphasizes the need for primary preventive measures early in life (Fig. 2). Together with the behavioral observations that life habits related to smoking and eating start in childhood, these findings impose the need for community programs aimed at children and adolescents (11). THE NEED FOR POPULATION CHANGE: THE SILENT MAJORITY CONCEPT OF COMMUNITY-ATTRIBUTABLE RISK
OR THE
Distribution curves of blood pressure in populations show that values in the range of “mild” hypertension occur much more frequently than severe blood pressure elevation. The same applies to cholesterol levels in high-cholesterol populations. In a WHO cooperative hypertension community study the number of registered mild hypertensives by far exceeded that of severe hypertensives (16). Although, as shown also by the Seven Countries Study (5), the individual risk is a curvilinear function of the risk factor level, steeply increasing at the upper end of the distribution, the community attributable risk, either computed in relative or in absolute terms (12), is considerably greater in the range of “mild” and “borderline” elevations than in overt disease. This may be stating the obvious, but the community health implications of this statement are not. In order to influence the “silent majority” of all those borderline and mild risk factor elevations, the distribution of the particular variable has to be changed in the whole community. This calls for setting up clear community (and public) health policies and for more epidemiological research. LIMITATIONS
OF COMMUNITY
HEALTH CARE
While the epidemiological findings in the above examples are rather clear-cut, the practical solutions community medicine offers are only partly satisfactory. Even the best mobile coronary care unit will be unable to reach those 30% of all subjects who die of acute ischemic heart disease suddenly or within a few minutes.
f complicated lesion r calcified lesion
Age group (years)
FIG. 2. Age distribution of atherosclerotic lesions in the left anterior descending coronary artery among 17,455 autopsy specimens examined in a WHO collaborative study in Czechoslovakia, Sweden, and the USSR.
SYMPOSIUM:
ATHEROSCLEROTIC
DISEASE
153
Hypertension community control programs, though successful in preventing complications of high blood pressure, imply the lifelong ingestion of chemicals by lo- 15% of all middle-aged people-clearly an ecological nonsense (13). Community programs for the prevention of rheumatic fever recurrences in developing countries struggle with low compliance and do not solve the problem of primary prevention. Intervention programs in children and adolescents have to operate in an environment infested by tobacco publicity, salty chips, and mountains of icecream in the midst of a risk factor pandemic in which the concept of primordial prevention-the preservation of populations as yet untouched by the risk factor epidemic (14)-is not even understood, no less accepted. It may be useful, therefore, to consider in greater depth the nature and limitations of community medicine. DISCUSSION
“The modern conception of community is very far removed from older conceptions based on the model of the village” (20). The community is rather like a field of force (in the sense of a magnetic field) exerting influence on people who, at the same time, are in the fields of many other forces as well (20). The limited, selfcontained, classical communities in the sense of Chinese agricultural communes or Israeli kibbutzim or, for that matter, a community like St. Helena (19) are rather exceptional phenomena in the modern world. It may be increasingly difficult to find communities with limited interactions like Farquhar’s three Californian towns (4). In a community intervention study in Yugoslavia it was not possible to find an informed city willing to play the role of a reference community (control group) once it became public knowledge that the city of Novi Sad would be the site of an intervention project. Communities of the type of “Peyton Place” are thus independent entities only as an abstraction. What then is a community from the health care research viewpoint? Let us try to take a functional approach, describing the usual chain of events, linking epidemiological information, populations, and health services. First, an epidemiological survey identifies the need for a particular intervention in a population (group). Guided by a number of pragmatic considerations, the intervention is then established in practice: the population thus covered represents the particular health care community. The next steps are to evaluate through epidemiological surveillance the changes induced by intervention and to feed the information back to the health services, possibly to modify the intervention methods. Epidemiological information thus has primacy over community intervention. The health care community depends on the scope of intervention. DO WE KNOW ENOUGH?
Do we know enough with regard to ischemic heart disease? Quoting Keys, “The epidemiological approach . . . initiated barely 30 years ago, has amply demonstrated great power in finding relationships, underlying clues to etiology, and suggesting preventive measures. But many relationships are proving to be more complex than first proposed” (5). The same applies, with even greater force, to health care research. Incomplete-
154
THOMAS STRASSER
ness of knowledge is no reason-and no excuse-to desist from action based on reasonable probabilities, but community intervention for the control of cardiovascular diseases should be subjected to continuing scrutiny. The final lesson for community medicine to be deduced from epidemiology is the need for a good information base, implying also further research in epidemiology. REFERENCES 1. Breslow, L. The contribution of epidemiology, in “Epidemiology and Health” (W. W. Holland and S. Guilderdale, Eds.). Kimpton, London, 1977. 2. “Community Control of Hypertension. Methodological Considerations and Protocol of a WHO Cooperative Project.” CVDi74.3 (II) Appendix I, Geneva, 1973. 3. Community control of rheumatic heart disease in developing countries: (1) A major public health problem: (2) Strategies for prevention and control. WHO Chron. 34, 395 (1980). 4. Farquhar, J. W., Maccoby, W., Wood, P. D., et al. Community education for cardiovascular health. Lancer 1, 1192-1195 (1977). 5. Keys, A. “Seven Countries. A Multivariate Analysis of Death and Coronary Heart Disease.” Harvard Univ. Press, Cambridge, 1980. 6. Lilienfeld, D. E. Definitions of epidemiology. Amer. J. Epidemiol. 107, 87 (1973). 7. Morris, J. N. “Uses of Epidemiology,” 3rd ed. Churchill Livingstone, Edinburgh/London/New York, 1975. 8. National High Blood Pressure Education Program. “Handbook for Improving High Blood Pressure Control in the Community.” National Heart, Lung, and Blood Institute. DHEW Publication. No. (NIH) 77-1086. 9. Shine, I. “Serendipity in St. Helena. A Genetical and Medical Study of an Isolated Community.” Pergamon Press, Oxford, 1970. 10. Strasser, T. Community control of hypertension-International activities. Heatth Serv. Rep. 88, 387-390 (1973). 11. Strasser, T. Primary prevention: The role of the World Health Organization, in “Childhood Prevention of Atherosclerosis and Hypertension” (R. M. Lauer and R. B. Shekelle, Eds.). Raven Press, New York, 1980. 12. Strasser, T. Hypertension research related to health care, in “Hypertension Related to Health Care-Research Priorities. Report on a WHO Consultation,” pp. 24-54. EURO Reports and Studies 32, Copenhagen, 1980. 13. Strasser, T. Hypertension: A public health challenge, in “Essential Hypertension” (R. H. Thurm, Ed.). Symposia Specialists Inc., Miami, 1979. 14. Strasser, T. Reflection on cardiovascular disease. Interdiscip. Sci. Rev. 3, 225-230 (1978). 15. Strasser, T., Dondog, N., El Kholy, A., Gharagozloo, R., et al. The community control of rheumatic fever and rheumatic heart disease: Report of a WHO international cooperative project. Bull. World Health Org. 59, 285-294 (1981). 16. Strasser, T., Dowd, E., and Duppenthaler, J. Mild hypertension in the community, in “Mild Hypertension: Natural History and Management” (F. Gross and T. Strasser, Eds.). Pitman Medical, Tunbridge Wells, 1979. 17. Vanecek, R. Atherosclerosis of the coronary arteries in five towns. Bull. World Health Org. 53, 509-518 (1976). 18. Wilhelmsen, L., Svardsudd, K., and Berglund, G. Development of high blood pressure and its consequences for health. A Swedish population study, in “Epidemiology of Arterial Blood Pressure” (H. Kesteloot and J. V. Joossens, Eds.), pp. 311-324. Developments in Cardiovascular Medicine, Vol. 8. Nijhoff, Hague/Boston/London, 1980. 19. World Health Organization. Myocardial infarction community registers, in “Public Health in Europe 5.” WHO Regional Office for Europe, Copenhagen, 1977. 20. Worseley, P. “Introducing Sociology.” Penguin, New York, 1970.
12, 150- 154 (1983)
MEDICINE
Implications
of Epidemiology THOMAS
World Health
Organization,
for Community
Medicine’
STRASSER CH-1211 Geneva 27, Switzerland
Although both epidemiology and community medicine are difftcult to define, the relationship between them can be described in practical terms. Examples are given in which cardiovascular epidemiological studies demonstrated the need (a) for improving existing community health care services, (b) for extending them, (c) for transposing them to new settings, (d) for starting preventive measures early in life, and (e) for inducing population-wide changes. However, community medicine has many limitations, calling for a better information base, and also calling for more epidemiological research.
EPIDEMIOLOGY
AND COMMUNITY
MEDICINE
Epidemiology has been called “the basic science of community medicine” (7). Conversely, community medicine has been regarded as “the practice arm of epidemiology” (1). Thus it is seemingly easy to describe the relationship between epidemiology and community medicine despite the difficulties of defining epidemiology itself (6) and despite the fact that “sociologists and others have already expended a great deal of effort in trying to define community without reaching any appreciable degree of consensus” (20). I shall try to describe this relationship, using examples of cardiovascular prevention studies in which I have personal experience. THE NEED FOR IMPROVING EXISTING COMMUNITY HEALTH CARE: DELAYS OCCURRING BEFORE REACHING MEDICAL CARE FOR ACUTE MYOCARDIAL INFARCTION
In a study of incidence of acute myocardial infarction (19), an analysis was made of the time elapsed from the onset of symptoms to various events in health care. Figure 1 shows, for selected communities, the median times between the beginning of the attack and the call for medical help, the first examination, and hospital admission. These times, very different in various communities, are indicative of the efficiency of emergency care for patients with acute myocardial infarctionand show which links in the health care chain were the weakest at the time of the study. It can be concluded in one case that the education of the public need be reinforced; in another, that the ambulance services need revision; and in a third case, physician responsiveness in this community needs improvement as well. THE NEED FOR EXTENDING COMMUNITY HEALTH CARE: HYPERTENSION COMMUNITY CONTROL PROGRAMS
In the late 1960s and early 1970s a number of surveys in various parts of the world established the fact, surprising to clinicians, that blood pressure was indeed ’ Presented at the International Symposium Disease, June 24-26, 1981, Anacapri, Italy.
on Epidemiology
150 0091.7435/83/010150-05$03.00/O Copyright All rights
@ 1983 by Academic Press, Inc. of reproduction in any form reserved.
and Prevention
of Atherosclerotic
SYMPOSIUM:
ATHEROSCLEROTIC
DISEASE
151
GO Ta so He L" Bu Be
0
100
200
300
400
500 min.
FIG. 1. Median time elapsed since onset of heart attack in seven European communities. There are considerable dilferences between the structures of hospital admission delay. Go is Goteborg, Sweden; Ta is Tampere, Finland; Bo is Boden, Sweden: He is Helsinki, Finland; Lu is Lublin, Poland: Bu is Bucharest, Romania; Be is Berlin, German Democratic Republic.
under control in only a small fraction of hypertensive subjects. Since the positive effect of hypertension treatment had been demonstrated, the obvious conclusion was that health care needed to be extended to all hypertensives in the community, and hypertension community control programs such as the WHO Cooperative Project (2) or the U.S. National High Blood Pressure Education Program (8) were instituted. Such programs have, indeed, reduced the proportion of untreated and undiagnosed hypertensives in the project communities. TRANSPOSING SETTINGS:
ESTABLISHED PREVENTIVE MEASURES TO NEW RHEUMATIC FEVER PREVENTION PROGRAMS IN DEVELOPING COUNTRIES
The effectiveness of penicillin prevention of rheumatic fever recurrences became evident in a number of community studies in the U.S. soon after the advent of penicillin. In the 1960s it also became increasingly obvious that rheumatic fever, by this time tending to disappear from affluent countries (although persisting in Western slums), was an important public health problem in developing countries. It had to be assessed whether the prevention of rheumatic heart disease in those developing, mainly tropical and subtropical, countries indeed required community control programs, and whether these were feasible and justified as well. A multicenter cooperative community project coordinated by WHO in nine developing countries (3) has shown that the cost of penicillin dispensed for prevention was amply discounted by the hospital days averted. All other benefits presented a net gain (15). THE NEED FOR AN EARLY START: ATHEROSCLEROSIS AND ITS PREVENTION IN YOUTH
A population-based anatomical study in five European towns, organized by WHO in the late 1960s (IO), confirmed that coronary atherosclerosis is considerably more prevalent than clinically manifest ischemic heart disease. A finding of capital importance was that the process started early: some 10% of boys and girls aged 10 to 14 already had raised atherosclerotic lesions in the coronary arteries-a
152
THOMAS
STRASSER
finding that forcefully emphasizes the need for primary preventive measures early in life (Fig. 2). Together with the behavioral observations that life habits related to smoking and eating start in childhood, these findings impose the need for community programs aimed at children and adolescents (11). THE NEED FOR POPULATION CHANGE: THE SILENT MAJORITY CONCEPT OF COMMUNITY-ATTRIBUTABLE RISK
OR THE
Distribution curves of blood pressure in populations show that values in the range of “mild” hypertension occur much more frequently than severe blood pressure elevation. The same applies to cholesterol levels in high-cholesterol populations. In a WHO cooperative hypertension community study the number of registered mild hypertensives by far exceeded that of severe hypertensives (16). Although, as shown also by the Seven Countries Study (5), the individual risk is a curvilinear function of the risk factor level, steeply increasing at the upper end of the distribution, the community attributable risk, either computed in relative or in absolute terms (12), is considerably greater in the range of “mild” and “borderline” elevations than in overt disease. This may be stating the obvious, but the community health implications of this statement are not. In order to influence the “silent majority” of all those borderline and mild risk factor elevations, the distribution of the particular variable has to be changed in the whole community. This calls for setting up clear community (and public) health policies and for more epidemiological research. LIMITATIONS
OF COMMUNITY
HEALTH CARE
While the epidemiological findings in the above examples are rather clear-cut, the practical solutions community medicine offers are only partly satisfactory. Even the best mobile coronary care unit will be unable to reach those 30% of all subjects who die of acute ischemic heart disease suddenly or within a few minutes.
f complicated lesion r calcified lesion
Age group (years)
FIG. 2. Age distribution of atherosclerotic lesions in the left anterior descending coronary artery among 17,455 autopsy specimens examined in a WHO collaborative study in Czechoslovakia, Sweden, and the USSR.
SYMPOSIUM:
ATHEROSCLEROTIC
DISEASE
153
Hypertension community control programs, though successful in preventing complications of high blood pressure, imply the lifelong ingestion of chemicals by lo- 15% of all middle-aged people-clearly an ecological nonsense (13). Community programs for the prevention of rheumatic fever recurrences in developing countries struggle with low compliance and do not solve the problem of primary prevention. Intervention programs in children and adolescents have to operate in an environment infested by tobacco publicity, salty chips, and mountains of icecream in the midst of a risk factor pandemic in which the concept of primordial prevention-the preservation of populations as yet untouched by the risk factor epidemic (14)-is not even understood, no less accepted. It may be useful, therefore, to consider in greater depth the nature and limitations of community medicine. DISCUSSION
“The modern conception of community is very far removed from older conceptions based on the model of the village” (20). The community is rather like a field of force (in the sense of a magnetic field) exerting influence on people who, at the same time, are in the fields of many other forces as well (20). The limited, selfcontained, classical communities in the sense of Chinese agricultural communes or Israeli kibbutzim or, for that matter, a community like St. Helena (19) are rather exceptional phenomena in the modern world. It may be increasingly difficult to find communities with limited interactions like Farquhar’s three Californian towns (4). In a community intervention study in Yugoslavia it was not possible to find an informed city willing to play the role of a reference community (control group) once it became public knowledge that the city of Novi Sad would be the site of an intervention project. Communities of the type of “Peyton Place” are thus independent entities only as an abstraction. What then is a community from the health care research viewpoint? Let us try to take a functional approach, describing the usual chain of events, linking epidemiological information, populations, and health services. First, an epidemiological survey identifies the need for a particular intervention in a population (group). Guided by a number of pragmatic considerations, the intervention is then established in practice: the population thus covered represents the particular health care community. The next steps are to evaluate through epidemiological surveillance the changes induced by intervention and to feed the information back to the health services, possibly to modify the intervention methods. Epidemiological information thus has primacy over community intervention. The health care community depends on the scope of intervention. DO WE KNOW ENOUGH?
Do we know enough with regard to ischemic heart disease? Quoting Keys, “The epidemiological approach . . . initiated barely 30 years ago, has amply demonstrated great power in finding relationships, underlying clues to etiology, and suggesting preventive measures. But many relationships are proving to be more complex than first proposed” (5). The same applies, with even greater force, to health care research. Incomplete-
154
THOMAS STRASSER
ness of knowledge is no reason-and no excuse-to desist from action based on reasonable probabilities, but community intervention for the control of cardiovascular diseases should be subjected to continuing scrutiny. The final lesson for community medicine to be deduced from epidemiology is the need for a good information base, implying also further research in epidemiology. REFERENCES 1. Breslow, L. The contribution of epidemiology, in “Epidemiology and Health” (W. W. Holland and S. Guilderdale, Eds.). Kimpton, London, 1977. 2. “Community Control of Hypertension. Methodological Considerations and Protocol of a WHO Cooperative Project.” CVDi74.3 (II) Appendix I, Geneva, 1973. 3. Community control of rheumatic heart disease in developing countries: (1) A major public health problem: (2) Strategies for prevention and control. WHO Chron. 34, 395 (1980). 4. Farquhar, J. W., Maccoby, W., Wood, P. D., et al. Community education for cardiovascular health. Lancer 1, 1192-1195 (1977). 5. Keys, A. “Seven Countries. A Multivariate Analysis of Death and Coronary Heart Disease.” Harvard Univ. Press, Cambridge, 1980. 6. Lilienfeld, D. E. Definitions of epidemiology. Amer. J. Epidemiol. 107, 87 (1973). 7. Morris, J. N. “Uses of Epidemiology,” 3rd ed. Churchill Livingstone, Edinburgh/London/New York, 1975. 8. National High Blood Pressure Education Program. “Handbook for Improving High Blood Pressure Control in the Community.” National Heart, Lung, and Blood Institute. DHEW Publication. No. (NIH) 77-1086. 9. Shine, I. “Serendipity in St. Helena. A Genetical and Medical Study of an Isolated Community.” Pergamon Press, Oxford, 1970. 10. Strasser, T. Community control of hypertension-International activities. Heatth Serv. Rep. 88, 387-390 (1973). 11. Strasser, T. Primary prevention: The role of the World Health Organization, in “Childhood Prevention of Atherosclerosis and Hypertension” (R. M. Lauer and R. B. Shekelle, Eds.). Raven Press, New York, 1980. 12. Strasser, T. Hypertension research related to health care, in “Hypertension Related to Health Care-Research Priorities. Report on a WHO Consultation,” pp. 24-54. EURO Reports and Studies 32, Copenhagen, 1980. 13. Strasser, T. Hypertension: A public health challenge, in “Essential Hypertension” (R. H. Thurm, Ed.). Symposia Specialists Inc., Miami, 1979. 14. Strasser, T. Reflection on cardiovascular disease. Interdiscip. Sci. Rev. 3, 225-230 (1978). 15. Strasser, T., Dondog, N., El Kholy, A., Gharagozloo, R., et al. The community control of rheumatic fever and rheumatic heart disease: Report of a WHO international cooperative project. Bull. World Health Org. 59, 285-294 (1981). 16. Strasser, T., Dowd, E., and Duppenthaler, J. Mild hypertension in the community, in “Mild Hypertension: Natural History and Management” (F. Gross and T. Strasser, Eds.). Pitman Medical, Tunbridge Wells, 1979. 17. Vanecek, R. Atherosclerosis of the coronary arteries in five towns. Bull. World Health Org. 53, 509-518 (1976). 18. Wilhelmsen, L., Svardsudd, K., and Berglund, G. Development of high blood pressure and its consequences for health. A Swedish population study, in “Epidemiology of Arterial Blood Pressure” (H. Kesteloot and J. V. Joossens, Eds.), pp. 311-324. Developments in Cardiovascular Medicine, Vol. 8. Nijhoff, Hague/Boston/London, 1980. 19. World Health Organization. Myocardial infarction community registers, in “Public Health in Europe 5.” WHO Regional Office for Europe, Copenhagen, 1977. 20. Worseley, P. “Introducing Sociology.” Penguin, New York, 1970.