Epidemiology and Air Pollution (1985) / Chapter Skim
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4 CONCEPTS AND STRATEGIES IN PLANNING EPIDEMIOLOGIC STUDIES ON AIR POLLUTION
4 CONCEPTS AND STRATEGIES IN PLANNING EPIDEMIOLOGIC STUDIES ON AIR POLLUTION
Pages 127-164
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From page 127... ...
The need for precision makes it necessary to seek out appropriately sensitive research tools and methods that will be capable of linking today's exposure with today's and tomorrow's health effects. This discussion of research strategies for the epidemiologic study of air pollution is guided by several principles.
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From page 128... ...
Fifth, the link between epidemiology and regulation will be a two-way street, with research planning illuminated by a clear understanding of the practical issues and constraints involved in regulation, and the regulatory process influenced by the product and capabilities of research. COMMUNICATION OF EPIDEMIOLOGY WITH OTHER RESEARCH DISCIPLINES Optimal use of the epidemiologic approach requires that it communicate with the parallel disciplines of clinical research and animal toxicology.
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From page 129... ...
Major air pollution research questions seldom emerge ab initio from the intellects of creative scientists. Most are public health questions that are developed through interplay of the interests and capabilities of the scientific community with extrascientific forces, such as the availability of research funds and the regulatory process.
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From page 130... ...
As in all scientific disciplines, epidemiologic research questions begin in a rather general form and are pruned to testable hypotheses that form the basis for design of individual studies. Every epidemiologic study of the adverse health effects of air pollution has to be crafted around the pollutant in question and the adverse effect under consideration.
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From page 131... ...
The relation of this question to air pollution concerns is indirect, however, except for its role in identifying study populations on the basis of contrasting disease patterns. Question 2, about the pathogenesis and natural history of a disease, can be answered through clinical observation and through epidemiology; but this
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From page 132... ...
It is reasonable to presume that, in most populations without extreme exposure, relative risks of overt clinical disease associated with air pollution are of low to moderate magnitude (approximately 1.2-3.0)
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From page 133... ...
Larger exposures can be studied to construct models that simulate the behavior of pollutants at lower dosages, but the reliability of mathematical extrapolation is limited by its dependence on unavoidable and untestable assumptions about the dose-response relationships. Future studies will gradually become better at providing quantitative information about the relationships between air pollutants and health, if the techniques for assessing exposure and effect mentioned in this report are developed and if research planning is appropriate.
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From page 134... ...
CONSIDERATIONS IN STUDY DESIGN, ANALYSIS, AND INTERPRETATION Epidemiologic projects concerning air pollution are among the most difficult to design. One reason is that ambient air pollution adds small increments to the respiratory morbidity risks of large masses of people, rather than large increments to the risks of a few.
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From page 135... ...
The complexity of the relationships among all the variables that could affect results of air pollution studies has two important implications: • Study design and planning require expertise regarding the concepts of epidemiologic research design. • The success or failure of future studies will depend increasingly on how well exposure, effect, and confounding variables have been characterized during study planning.
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From page 136... ...
A few relevant concepts are introduced in Appendix C to point out the particular challenges for air pollution studies. AVAILABLE METHODS FOR EPIDEMIOLOGIC STUDIES Epidemiology depends on a small number of distinct study methods, any of which can be applied to air pollution questions.
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From page 137... ...
Inferences based on ecologic studies tend to be much weaker, and there is a much greater loss of information than when individual data are used. Ecologic studies can involve comparison of exposure and disease rates over time in the same population (temporal studies)
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From page 138... ...
Although workplaces have sometimes routinely collected data that allow reconstruction of exposure, few such data exist for community exposure to air pollutants. Techniques for reconstructing pollution exposure, perhaps based on residential histories, remain to be developed.
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From page 139... ...
The statistical-power relationships involved in longitudinal measurements of lung function in groups of various sizes for various periods have been analyzed recently by Berry (see Table 1, in Chapter 5 ) .2 The cost and information value of these options must be explored in the planning of longitudinal studies.
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From page 140... ...
Early disease markers might also provide outcome measures that are more frequent than overt disease and thus magnify relative risk and increase the statistical power of cohort studies. The success of the Framingham and Tecumseh studies has led to widespread appreciation of the value of longitudinal cohort studies in identifying biologic and lifestyle measurements that predict disease in groups.
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From page 141... ...
Some studies have suggested that one-time cross-sectional evaluations of adverse health effects, such as lung function deficits and respiratory symptoms, are less sensitive than longitudinal evaluations of changes over time. Crosssectional study of adults in Berlin, New Hampshire, in 1962 showed no greater prevalence of symptoms in those residing in more polluted areas; however, a followup study in 1967 indicated that improvements in air quality had led to detectable improvements in symptom prevalence.6 Studies by Van Der Lende in the Netherlands have suggested that longitudinal measurement of lung function is a more sensitive indicator of air pollution effects than cross-sectional measurement.25 In fact, there are puzzling discrepancies in the normal relationship between age and lung function, depending on whether curves are obtained by cross-sectional or by longitudinal methods.7 The choice between cross-sectional and longitudinal approaches is affected to some degree by the difference between the fluctuation in exposures or effects from person to person and the fluctuation from time to time for the same person.
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From page 142... ...
The problems lie in defining the disease, measuring past exposures reliably, selecting the control group, and handling confounders in the analysis. The prevalence of exposure to a suspected agent is the important determinant of sample size and hence study sensitivity, but rarity of the disease is usually not a hindrance in this approach if enough cases can be found, even if from multiple sources.
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From page 143... ...
This strategy was used by investigators in England after the Clean Air Act in 1956 caused a great reduction in air pollution in most urban areas. The investigators tracked disease rates and compared them over time with the changing degree of air pollution and found that areas with greater reductions in smoke pollution experienced greater declines in lung cancer death rates.14
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From page 144... ...
The direct, deliberate design and organization of traditional epidemiologic studies are only part of what is required for an effective air pollution research strategy. The other part is the recognition and use of these special, and perhaps fleeting, situations for study.
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From page 145... ...
Kilburn and co-workers, after a study designed to examine the effects of para-occupational exposure to asbestos on wives and daughters of shipyard workers, reported the serendipitous finding of an effect on pulmonary function that might have been due to ambient air pollution.11
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From page 146... ...
PRISTINE POPULATIONS We accept some air pollution as an inevitable accompaniment of contemporary industrial society, but we have only scant knowledge about the general health status that we might observe if we had little or none at all. In particular, the shapes of growth and decay curves for lung function in the absence of substantial air pollution are not known.
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From page 147... ...
population.19 As Rose has recently stated, the most difficult risk factor to detect epidemiologically is one that is present in every member of the population.23 POINT-SOURCE POLLUTION In communities near single point sources of pollution, collection of precise data on emission and exposure modeling of the population are often feasible. Moreover, the population at risk is often well-defined and might be contained within administrative units conducive to the organization of an epidemiologic study.
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From page 148... ...
CONCEPTS AND STRATEGIES IN PLANNING EPIDEMIOLOGIC STUDIES ON AIR 148 POLLUTION FIGURE 6 SO2 in cities of the GEMS monitoring network, 1976-1980. Range of annual averages at individual sites and composite average for each city.
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From page 149... ...
For example, sulfate concentration might be high in the presence of low concentrations of particles or ozone, or nitrogen oxide concentration might be high in the presence of low concentrations of other photochemical oxidants. It is important to maximize the benefit derived from expensive longitudinal studies and to disseminate their methods and results as widely as possible.
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From page 150... ...
. ADAPTATION OF EXISTING COHORT STUDIES The remaining special opportunities concern the design of highly powerful and cost-effective epidemiologic studies through adaptation or "piggy-backing" of air pollution hypotheses onto longitudinal studies or surveys.
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From page 151... ...
The health component of the HIS includes questions on acute illnesses during a 2-week period before the interview and on chronic illnesses. Although acute respiratory diseases have recently been studied in this manner, the utility of the HIS data for studies of the relation between air pollution and chronic disease remains to be explored.21 Another survey conducted by NCHS, the National Health and Nutrition Examination Survey (NHANES)
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From page 152... ...
Estimating the productivity and costeffectiveness of various ways to answer specific questions has become an integral part of epidemiologic research planning. For this purpose, benefits are usually conceived of as information value -- the degree to which the study's results bridge the gap between the question and its definitive answer or provide spinoff knowledge for other studies.
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From page 153... ...
A research program that aims to produce the best possible epidemiologic studies will have to include funding for complementary nonepidemiologic research, including methodologic and technical development and exposure characterization. Technologic research and development, designed to provide better tools for exposure and effect assessment, must be closely woven into epidemiologic research strategies.
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From page 154... ...
Successful examples of long-term studies include the 25-year British study of a cohort of children from birth to young adulthood and the Harvard Air Pollution Health Study of the growth and decay of lung function.5 26 The need for administrative and financial stability also applies to a sequence of closely linked studies. The Environmental Protection Agency's record of support for epidemiologic studies since 1970 is one of cataclysmic variation, from strong support to nearly complete withdrawal of funds, in spite of heavy reliance on epidemiologic research for risk assessment and standard-setting.
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From page 155... ...
However, a portion of the epidemiologic research program should have the flexibility to respond quickly to short-lived opportunities or demands and in so doing work closely with research sponsors and regulators. The expertise for designing and conducting epidemiologic studies of air pollution is a rare resource that, once established, needs to be cultivated and maintained.
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From page 156... ...
EPIDEMIOLOGIC DATA AND THE REGULATORY PROCESS At the heart of the regulatory process for ambient air pollutants in the United States is the determination of approximate "safe" exposures to specific pollutants. In some instances, for some aspects of the standards, epidemiologic data can provide the direct basis for such determination.
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From page 157... ...
There are several reasons for the difference: statistical power of studies might be adequate to show large effects, if they are present, but not to exclude smaller effects that are of regulatory interest; nonrandom errors might be more easily dealt with in positive studies; clear demonstration of an effect in one population segment might create a presumption of effects elsewhere that is not balanced by similarly clear demonstration of the lack of effects in other segments; and control measures might be required if a small part of the population is affected, but not rendered superfluous if a large part is shown to be unaffected. Thus, good large studies with negative results can often have less meaning
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From page 158... ...
A genetic-epidemiologic study of chronic obstructive pulmonary disease: 1. Study design and preliminary observations.
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From page 159... ...
Uses of ecologic analysis in epidemiologic research.
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From page 160... ...
The effect of migration on comparison of disease rates in geographic studies in the United States.
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From page 161... ...
CONCEPTS AND STRATEGIES IN PLANNING EPIDEMIOLOGIC STUDIES ON AIR 161 POLLUTION 26. Ware, J.H., Thibodeau, L.A., F.E.
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From page 163... ...
163 Chapter 5 The Application of Epidemiology to Selected Research Questions
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