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(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.



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