Environmental Epidemiology, Volume 2 Use of the Gray Literature and Other Data in Environmental Epidemiology (1997) / Chapter Skim
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2 Environmental-Epidemiology Studies: Their Design and Conduct
2 Environmental-Epidemiology Studies: Their Design and Conduct
Pages 12-25
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From page 12... ...
We recommend that research on study designs focus on the improvement of statistical power or probability of detecting an effect. Finally, we review principles for inferring causation in epidemiology.
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From page 13... ...
DESCRIPTIVE STUDIES Descriptive studies include case reports, surveillance systems, ecologic studies, and cluster studies (WHO, 1983~. Case Reports A case report is a descriptive study of a single individual or small group in which the study of an association between an observed effect and a specific environmental exposure is based on detailed clinical evaluations and histories of the individualist.
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From page 14... ...
If these exposure registries are to produce valuable results, they will need to include sufficient numbers of persons over a long enough period for diseases of interest to manifest themselves in numbers sufficient to demonstrate that some problem exists or that the problem is unlikely to exist and be large enough to cause serious concern. Ecologic Studies Ecologic studies explore the statistical connection between disease and estimated exposures in population groups rather than individuals.
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From page 15... ...
Ecologic studies suffer from serious weaknesses: they assign group exposure levels to all members of the group, fail to control for individual confounding factors, use necessarily crude estimates of exposure, and may not capture the relevant exposure at the time of disease induction. A1though some population groups in ecologic studies may appear similar to "cohorts" (see below)
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From page 16... ...
Information from medical records, clinical or laboratory investigations, questionnaire results, or direct measures or estimates of exposures may allow analytic studies to explore hypotheses about suspected causes of disease or identify and measure risk factors that increase the chance that a given disease will occur. Analytic studies may also be a source of additional specific hypotheses, often leading to a sequence of studies, the more recent being designed to attempt to refute hypotheses raised by earlier studies.
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From page 17... ...
cohort study relates a complete set of outcomes already observed in a defined population to exposures that occurred earlier; data on both exposure and outcomes must be available at the time the study is undertaken. Prospective cohort studies, in which current exposure is directly measured
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From page 18... ...
Short-term fluctuations in those outcomes are correlated with short-term variations in environmental exposures. For instance, studies of changes in peak respiratory flow, respiratory symptoms, hospital admission, and daily mortality can be linked to changes in environmental air pollution.
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From page 19... ...
Many of the risk factors of interest derive from large-scale data sets on environmental pollution that involve continuous variables, as well as a variety of clinical health indicators. Much of cancer epidemiology has focused on studying specific anatomic sites of cancer and delineating important contributors to specific types of cancer, such as the link between occupational exposure to benzene and leukemia or that between asbestos and mesothelioma.
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From page 20... ...
In the absence of adequate implementation of both aspects, the term molecular epidemiology should not be used. CONSIDERATIONS OF THE POWER OF STUDY DESIGNS Before any study is undertaken, sound epidemiologic practice requires careful consideration of statistical power, that is, the probability that a given research study will be able to detect a true positive effect if it exists.
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From page 21... ...
Statistical tests cannot determine whether or not an error has been made but can indicate the probability that an error could occur, called beta, if the effect is of some hypothetical size specified by the investigator. The power to detect an effect of that size, defined as 1-beta, depends on the alpha level of significance testing and the unknown relative risk.
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From page 22... ...
, the stronger the association between the inferred link of exposure to disease for exposed individuals. For example, an RR of 1.4 for lung cancer after exposure to environmental tobacco smoke indicates that exposed persons are 40% more likely to develop lung cancer than are nonexposed persons.
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From page 23... ...
can have many causes, and single agents can cause many effects (e.g., lead at high-enough levels can cause increased blood pressure, neurologic symptoms, reproductive effects, and kidney damage)
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BIOLOGIC PLAUSIBILITY The relation between the suspected causal agent and suspected effect should make sense, given the current understanding of human biology. Animal studies or other experimental evidence can strengthen or weaken the biologic plausibility of the relation by demonstrating mechanisms of disease or determining whether the association between exposure and disease holds in experimental situations.
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From page 25... ...
V Additional studies of the relation of fluoride domestic waters to dental caries experiences in 4425 white children aged 12-14 years, of 13 cities in 4 states.
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