v) Studies of individuals are prone to the opposite of the ecological fallacy, the so-called a) environmental fallacy b) atomistic fallacy c) cross-sectional studies d) clinical trials.
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Answer:
Abstract
The validity of ecological studies in epidemiology for inferring causal relationships has been widely challenged as observed associations could be biased by the Ecological Fallacy. We reconsider the important design components of ecological studies, and discuss the conditions that may lead to spurious associations. Ecological associations are useful and valid when the ecological exposures can be interpreted as Instrumental Variables. A suitable example may be a time series analysis of environmental pollution (e.g. particulate matter with an aerodynamic diameter of <10 micrometres; PM10) and health outcomes (e.g. hospital admissions for acute myocardial infarction) as environmental pollution levels are a cause of individual exposure levels and not just an aggregate measurement. Ecological exposures may also be employed in situations (perhaps rare) where individual exposures are known but their associations with health outcomes are confounded by unknown or unquantifiable factors. Ecological associations have a notorious reputation in epidemiology and individualistic associations are considered superior to ecological associations because of the “ecological fallacy”. We have argued that this is incorrect in situations in which ecological or aggregate exposures can serve as an instrumental variable and associations between individual exposure and outcome are likely to be confounded by unmeasured variables.
Keywords: Aggregate studies, Bias, Ecological fallacy, Environmental health, Instrumental variables, Methodological individualism
Introduction
Ecological studies are epidemiological investigations in which either the units of analysis are populations or groups of people, as opposed to individuals, or exposures are only known at the population level while outcomes may be known at the individual level. Specifically, ecological variables are properties of groups, organisations, or places, whereas individual-level variables are properties of each person [1]. Generally, public and environmental health researchers utilise ecological study designs to explore potential causal associations between one or more exposures and a specific health outcome when alternative study designs (e.g. case–control, cohort, randomised controlled trial) are not possible or relevant. For example, an ecologic study is the most appropriate research design if we were interested in the effect of a macro-level governmental policy change, such as an inner-city traffic congestion charge to reduce carbon emissions and improve air quality, on a particular aggregate health outcome (e.g. number of consultations for childhood respiratory disorders).
Ecological fallacy
An ecological study design may also be utilised when the underlying question regards individuals, such as when one is interested in the effects of air quality on health. In this context, ecological studies are potentially susceptible to the “ecological fallacy”; biases that may occur when an observed relationship between aggregated variables differs from the true, i.e. causal, association at an individual level [2]. Indeed, since Robinson in 1950 showed that correlations on an individual level can differ markedly from those on an aggregate, ecological level, epidemiological textbooks, papers and courses have warned us about the dangers of this ecological fallacy