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Health is everybody's natural concern, and an everyday theme in the media. Outbreaks of disease such as the most recent influenza, occurring in many countries at the same time, make front-page news. Beyond epidemics, novel findings on dangerous pollutants in the environment, substances in food which prevent cancer, genes predisposing to disease or drugs promising to wipe them out, are reported regularly. Their actual relevance for human health depends crucially on the accumulation of evidence from studies, guided by the principles of epidemiology that directly observe and evaluate what happens in human populations and groups.

These studies combine two features. They explore health and disease with the instruments of medical research, ranging from records of medical histories to measures of height, weight, blood pressure to a wide variety of diagnostic tests and procedures. At the same time they involve individuals living in society exposed to a multitude of influences, and they cannot be conducted in the isolated and fully controlled conditions of laboratory experiments. Their design, conduct and analysis require, instead, the methods of statistics and of social sciences such as demography, the quantitative study of human populations. Without a clear understanding of this composite nature of epidemiology and of its reasoning in terms of probability and statistics it is hard to appreciate the strengths and weaknesses of the scientific evidence relevant to medicine and public health that epidemiology keeps producing. It is not only among the general public that a woolly appreciation or even a frank misreading of epidemiology often surfaces, for instance in debates on risks or on the merit, real or imagined, of a disease treatment. In my experience the same may occur with journalists, members of ethics committees, health administrators, health policy makers and even with experts in disciplines other than epidemiology responsible for evaluating and funding research projects.

(11) Epidemiology

Intro to Epidemiology Study Types

Virtual Library: Medicine and Health: Epidemiology



Empowering people

In an equal rights society, every citizen ought to be empowered to take part in decisions affecting her or his health and, through democratic processes, in deliberations concerning the health of the population. This can come about through information, conditioning, or education. There are innumerable sources of information: newspapers, magazines, books, television, and, most prominently, the Internet. There are close to 100,000 sites on the Web dealing with health matters and a major issue is the accuracy of the information. Studies are being done to measure the risk of encountering inaccurate sources, and private and public accreditation systems are being developed.

Almost everybody with access to the Web searches it occasionally or regularly on health, usually in relation to actual or possible health problems. Texts found for this reason or for curiosity or cultural interest need to be interpreted in the light of two considerations. First, most descriptions are inherently probabilistic, based as they must be on risks and rates of success of a preventive measure or of a treatment, or rates and risks of harm from side effects of a drug, from an unhealthy food, or from smoking marijuana, say.

Second, the presentation is usually influenced by who is providing the information and for what declared or implicit purpose. It may be impartial and strictly to the point or framed in a wider educational context (as the guidance for the wider public of the National Institute for Health and Clinical Excellence in the UK), or it may instead lean towards propaganda to condition people to buy and use some product often by heightening worries about health.

There are, however, some rules of thumb that may be usefully applied to screen health information from Web searches or in the media:

• Trust new findings only if replicated. Frequently repeated claims such as, for instance, that a newly identified protein in tomatoes reduces the risk of colon cancer by half, should be treated with great caution, not because the result arises from a flawed study (it could) but, as stressed many times in this book, because a causal link can only be established through replicated, separate, and concordant investigations. Replicated investigations means several different studies, not the result of the same study echoed with various delays by several different media.

• Trust only findings qualified by their uncertainty. We all prefer a black-and-white image of reality, if nothing else because decisions to be taken are perforce yes-or-no. Yet most often there is some margin of uncertainty in the results and black-and-white descriptions hide an essential part of the relevant information. Dogmatic statements should be treated with caution.

• Trust findings only if placed in context. Enabling people, in professional as in ordinary life, to transform information into empowering knowledge implies that information is not isolated nor randomly connected to other elements, but placed in context. For example, findings of studies on the possible cancer risks from mobile phone use should be discussed in the context of other health effects, including the risk of car accidents from use while driving. This can be done within the text itself or by links to external references. Such contextualization is essential in developing the reader's personal appropriation and interpretation of information; it does not substitute for it nor should it try to do so.

• Trust findings only if not framed as advertisements. Advertising is a signal necessary to draw attention to the substance, i.e. new or important findings. In commercial, sales-promoting reporting, however, the roles are completely reversed, the advertisement being the substance. Selling genetic profiles on the Web pretending, based on questionable or no evidence, to predict which diseases you will suffer in the future, has become a profitable enterprise. A safe rule would be to ignore it altogether: by ignoring such ventures, you lose nothing and when sound evidence about genetic factors predisposing to a disease becomes available, you will learn of them anyway from other, non-commercial sources.

• Trust findings and recommendations only if concordant. This is perhaps the most crucial guiding rule. With information, as with most other circumstances in life, there is no free meal; there are low-cost fast meals but they are of unknown quality. It is only by taking the time and effort of cross-checking the information from different sources, carefully looking at details, that one can be reasonably confident about the quality and validity of the information.

Health systems and public health

The health system is the common name for the complex of all activities directly dealing with health, although in most, if not all, countries this ensemble is more a complicated aggregate of many component systems than a unique organization. Public health coordination, itself one of the components operated chiefly by central, regional, and local health authorities, frames and interrelates the systems of hospitals (public, private for profit, private non-profit), general practices, clinical specialists, prevention units, and all other health-related activities.

Administrators at all levels of the health system, as well as political decision makers, constantly face the issue of comparing benefits and costs of interventions and services. Economic analyses may focus on exploring different ways of performing the same intervention, for instance the same number of renal dialyses, in order to identify the least costly procedure (cost-minimization analysis). Or they may compare the cost and the result, in terms of a common outcome like prolongation of life, of different interventions such as renal dialysis versus kidney transplant (cost-effectiveness analysis). Finally, they may compare costs and benefits of different interventions for the same or different conditions (hypertension treatment or influenza immunization?) in monetary terms or in some measure of `value' as perceived by individuals (cost-utility). Epidemiologists intervene in these analyses by providing evidence on health benefits and ill effects as evaluated by systematic reviews of biomedical and epidemiological studies. The same standard of rigorous scrutiny applied to this evidence also needs to be used for assessing the economic evidence. Short of this there is no guarantee that the health of all, including the most vulnerable, will stay ahead of other societal interests, industrial, financial, or ideological.

The ethics of epidemiological studies

The conduct of epidemiological studies poses ethical problems, particularly concerning the confidentiality of identifiable personal data and the use of stored blood samples to carry out genetic and other tests. To what extent can data in documents which clearly identify the individual, such as birth and death certificates, medical and prescription records, or employment records, be consulted for epidemiological research purposes? It has been the practice until the relatively recent past that epidemiologists would freely access these data, under a simple clause of personal engagement to guarantee that the person would not be identified by other parties. This clause would permit, for instance, the use of prescription records to form a cohort of subjects who used a drug suspected to induce kidney cancer as a side effect and, second, establishing, by linking the subjects' names to a mortality register, whether this cohort experienced a particularly high rate of kidney cancer. This type of practice has since come under criticism. It is argued that in all circumstances the consent of the individual is required to make the documents available for research purposes, the exception being a public health emergency, such as an epidemic, that necessitates rapid consultation of identifiable personal records. It is not only the ethical principle of doing good and not doing harm that needs to be respected by protecting the confidentiality of personal data, but also the principle of autonomy. Autonomy, i.e. freedom of self-determination, dictates that the individual to whom the personal data belong has, not exclusively, but certainly before anyone else, the right to decide whether and how the data can be used.

Rigid adherence to these principles may have the simple consequence of making epidemiological research impossible. Dead people cannot give consent and living people may be nearly impossible to trace and ask for consent many years after the documents of interest were produced. Ethics experts, national regulators, and international institutions such as the World Health Organization have taken different stances in respect to these issues. In some countries, it proves difficult to link documents because the personal identifiers, for example names or social security numbers, are deleted or masked. Roundabout ways of achieving the link without knowledge of the identity of the person may exist, but they are cumbersome and, worse, they may entail frequent errors, making studies unreliable. In general, however, the trend is towards regarding an epidemiological investigation even without consent as permissible provided that (a) an ethics committee independent of the researchers proposing the study and including lay people has approved the research; and (b) explicit and strict conditions are respected in the consultation and linkage of the documents.

Even more ethically problematic are the issues raised by the recent establishment of repositories of biological specimens, for instance blood, on which a theoretically limitless number of old and new biochemical and genetic tests can be performed. The very purpose of these repositories is to permit tomorrow epidemiological investigations that may improve our understanding of diseases using tests not yet available today. For this reason, it is impossible to ask the person who donates the blood to consent to research that even the investigator cannot yet specify. General consent `for medical research' is too wide to be regarded as `informed' and it may also induce refusals. It may, however, be acceptable as consent to the storage of the blood in the repository provided it is accompanied by the clause that each actual use of the blood will occur within a research project approved by an ethics committee. It will then behove the ethics committee to judge, depending on the nature of the project, whether or not it is necessary to go back to the subjects and obtain their consent. This may not be demanded for a study of breast cancer risk, but it may be for a project investigating the hypothesis that some genes are associated with proneness to commit crime. Similar issues arise for blood or other biological specimens collected from patients in hospitals and stored when later uses are outside research on the disease or diseases of the patient.

Finally, very delicate problems arise when moving from observational to intervention studies. What should be the comparison treatment in a randomized trial testing a new preventive vaccine in a country with poor health services?

The best current vaccine or a placebo, given the fact that in that country many or most people do not receive vaccines anyway? Although `realistic', the latter option appears very debatable because it accepts different ethical standards depending on who is going to be included in a trial: if the same or a similar experiment were to be carried out in a developed country (maybe the very one producing the medication), the use of a placebo instead of the best existing medication would not be accepted. Local adaptations of study designs are admissible, but bending of basic moral principles of universal value are not acceptable for a third general ethical principle, justice. Basic ethical principles for medical and health research are outlined in the `Declaration of Helsinki', a document periodically revised by the World Medical Association and first drafted in the aftermath of World War II to prevent the repetition of the criminal experiments practiced on the camp inmates by the Nazis.

As a rule, all study protocols have to be approved by an ethics committee, typically composed of a dozen health professionals, ethics specialists, and lay people independent of the researchers proposing the study. Projects that involve only completely anonymous data may not be subject to ethics committee approval if the procedures satisfy the requirements of the data-protection authorities. A universally accepted principle is that a project which is scientifically invalid, hence incapable of producing reliable information, is automatically unethical and not acceptable. The requirement is crystal clear but its application is often imperfect. Study protocols may arrive on the desk of the ethics committee without previous evaluation of their scientific validity by an expert committee, and the ethics committee has to act in a dual role of assessing both the scientific aspects, a task for which it has at best limited competence, and the ethical aspects. This is still the situation prevailing in many countries. It affects epidemiology in particular, as even basic literacy in the subject is thin and ethics committees may not clearly grasp the distinctions, entailing sharp differences in ethical requirements, between observational studies with anonymous data, observational studies with personal identifiable data, and intervention studies such as randomized population trials.


(12) Epidemiology


Food, Justice and Health Equity: Culture is Health- Sovereignty and Food Systems

Health and social justice - WHO

Justice, Inequality, and Health


Justice and health 

Whatever the type of study, the ethics committee's task focuses on guaranteeing the protection of the subjects included in the investigation. The committees rarely discuss to what extent a study responds to the health needs of the country where it is conducted, an issue particularly relevant for developing countries that implies but goes beyond ethics into the politics of research and health. Political choices in these domains must first of all confront the dramatic inequalities existing between developed and developing countries. By far the largest proportion of biomedical research funds is spent on diseases affecting the minority of the world population (less than one-fifth) living in the developed world.

According to some estimates, 10% of the total world burden of diseases attracts 90% of the biomedical research funds (the so-called `90/10 divide'). Similarly, almost 90% of the money destined for health care is spent in developed countries and only 10% in the developing countries, where the great majority of humankind lives. Although they are not the only determinants of health, these huge inequalities in investment and current expenditure involve vast disparities in health. A newborn in Africa can expect - if today's conditions do not improve - to live on average 30 years less than a newborn in North America or Europe. A child born in a country like Angola is more than 70 times more likely to die in the first few years of life than a child born in Norway, and a woman giving birth in sub-Saharan Africa is 100 times more likely to die in labour than a woman in a rich country. Early life and premature death is not only frequent in developing countries but may often be `invisible'. In India, only one-third of deaths are accurately registered and for only one-third of them is the cause recorded.

That the sheer chance of being born in a developed rather than in a developing country makes such huge differences in life span and healthy life is a blatant social injustice, all the more in a world that has never been as wealthy as today.

Have a vast divergence between a sustained increase in the income per person in a number of the most developed countries of the world and the quasi stagnant amounts of per capita transfers for economic development and welfare assistance to the developing countries during the 40 years between 1960 and the end of the 20th century. The trend in the new century has, however, been more favourable, particularly for the specific sub-sector of health assistance, notably thanks to the inflow of private donations from major charities. Against this background, the United Nations fixed, in 2000, eight broad `Millennium Development Goals' (MDGs) to be attained by the year 2015. All encompass multiple targets and have some relevance for health; and MDG 4 (reduce the number of deaths in children under 5 by two-thirds with respect to the 1990 level), MDG 5 (reduce the maternal mortality rate by three-quarters in respect to 1990), and MDG 6 (combat HIV/AIDS, malaria, and tuberculosis) focus specifically on health. So far, definite successes are on record, although at a pace unlikely to be sufficient to attain the goals by the 2015-2016 deadlines.

The key role of social determinants, including economic ones, for health not only in developing but also in developed countries has prompted the establishment by the World Health Organization of a Commission on Social Determinants of Health, whose landmark report `Closing the gap in a generation' was published in 2008.

To quote from the report:

Our children have dramatically different life chances depending on where they were born. In Japan or Sweden they can expect to live more than 80 years; in Brazil 72 years; and in one of several African countries, fewer than 50 years. And within countries, the differences in life chances are dramatic and are seen worldwide. The poorest of the poor have high levels of illness and premature mortality.

In fact, homeless people have a life span 20 or 30 years shorter than their fellow citizens living close by in their homes. The report also stresses that in countries at all levels of income, health and illness follow a social gradient: the lower the socio-economic position, the worse the health.

Health without limits?

Within a society, disease has always mobilized at the same time the care of the sick and powers, natural, religious, magic, to fight disease. In the wake of the 17th century's scientific revolution, both care for the patients and powers intended to fight disease became slowly but steadily based on scientific and technical knowledge. Two centuries of development of industrial capitalism produced a further gradual transformation in disease care, treatment, and prevention, reaching in the second half of the 20th century the stage of a mature `health industry', today one of the largest economic sectors in developed countries. Lately this has become, like most other sectors of the economy, tied to the speculative inventiveness of international finance, with immediately tangible adverse consequences. The Food and Agricultural Organization estimates that the current economic slowdown has brought the number of hungry people in the world above the bar of one billion and increased their proportion within the total world population. There is little doubt that unregulated finance, and more generally poorly regulated market forces, are important determinants of today's wide gaps in health conditions within and, much more, between countries. They are also responsible in other ways for a profit-driven rush to expanding health in developed countries.

One example is the offer via the Web of tests alleged to tell you whether your genes make you liable to the future occurrence of particular diseases. Common conditions like cancer, cardiovascular diseases, or diabetes are of course prime targets of the marketing strategy. The only sure thing is that the genetic tests are feasible and that you have to pay for them. How accurately they predict whether a disease will occur is for most of them neither declared nor known, and when the disease will occur is totally unknown. To advertise this approach as `prevention' is mystifying because, in addition, for several conditions such as many cancers there is no well-established preventive measure even if one were to know with absolute certainty that the disease will occur. A second example is disease-mongering, the widening of the definition of treatable diseases so that even the mildest and most dubious cases receive medical treatment. Variants of normal behaviours are then classified as diseases requiring treatment, like the condition of restless leg or generic female sexual dysfunction.

Both these examples have common traits. Under the thin cover of complying with the `right of people to know', they actually promote, for the sake of profit, dependency and suppression of critical judgment, of doctors by persuading them to prescribe drugs for people who could do without; of citizens by making them hungry for more tests, medical examinations, and medical remedies to pursue the mirage of unlimited health. These unhealthy trends go counter to the empowerment of people. A psychologist might say that they actually foster an `infantile regression' among people by subtly fuelling fear and the need for continuous reassurance against it.

Epidemiology for justice in health

A card-carrying epidemiologist once said, `today epidemiology is needed everywhere in medicine and public health'. Although formulated by an interested party, the statement is essentially correct. One major consequence is that no single person can competently master all or most areas of contemporary epidemiology and epidemiologists become specialized in particular fields of the discipline. Thus it is common to hear of genetic, environmental, social, cardiovascular, cancer, and paediatric epidemiology, and many other fields. Whatever their specialty, all epidemiologists share a common core of methods of investigation, of which these texts has attempted to give a bird's-eye view, and a population perspective of health.

The term `population', the trademark of epidemiology, however, covers two distinct aspects. First, population is the working tool of epidemiology, which uses populations to investigate diseases and health in the same way as other research uses mice, hamsters, or cell systems. The second aspect is people awaiting the reduction of their burden of diseases, and this may happen only to the extent that epidemiological research results are translated into effective interventions. Should epidemiologists use populations as expedient tools for science and do nothing about populations as targets for interventions simply because it is not their job as researchers? In academic circles this attitude is not uncommon: results of epidemiological research are best left at the door of colleagues in public health practice and of decision makers, allowing them to use the findings or not, as and when they see fit.

This attitude is objectionable on logical and ethical grounds. It contradicts the claim, very often advanced when requesting funds for epidemiological research, that because epidemiology directly studies humans, it can contribute more immediately than other biomedical research, for example experiments in the laboratory, to people's health.

It also deviates from the ethical principle that Immanuel Kant formulated in neat terms at the time of the Enlightenment: any human should never be regarded only as a means, as would be the case if populations were considered by epidemiologists only as research instruments. Ensuring that results of research are effectively translated into benefits for all people, reducing the social injustices in health, demands an active involvement which may take variable forms, from assistance to full participation in decision making, to social critiques, and to advocacy initiatives. There is no room for confusion between this involvement and the duty of scientific impartiality: when one's ethical and political values are openly declared, scientific impartiality and judgments become well separated from the value judgments inherent in any advocacy or involvement in policy making.

Epidemiology has evolved as a response to diseases in society and is not only the product of technical and scientific developments but, as for any other science, reflects to a variable extent the ideas prevailing in society at different historical times. Today, personal liberty for everybody is a dominant idea, value, and aspiration in society. However, it cannot be `for everybody' if it is not at least approximately an `equal liberty', without the huge differences in power and resources that exist between individuals. Among the resources that feed individual freedom, health is the most basic; our direct experience teaches us that without health personal freedom is severely restricted. Thus advancing justice in health by minimizing health inequalities within and between countries is the common aim of all streams of epidemiology and the acid test of its value to health. As John Rawls put it: `Justice is the first virtue of social institutions, as truth is of systems of thought'. Both are guiding lights for epidemiologists.



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