Ecological study
Encyclopedia
An ecological study is an epidemiological study in which the unit of analysis is a population rather than an individual. For instance, an ecological study may look at the association between smoking and lung cancer deaths in different countries. An ecological study is normally regarded as inferior to non-ecological designs such as cohort
and case-control studies because it is susceptible to the ecological fallacy
. An example of an ecological study is the analysis of the effects of disinfection byproducts on newborn babies, using 109 Massachusetts towns as units of analysis (Wright et al. 2004). (For an environmental definition of this term see Ecology
.)
Ecological studies can be easily confused with cohort studies, especially if different cohorts are located in different places. The difference is that in the case of ecological studies there is no information available about the individual members of the populations compared (e.g. comparing several states based on state-wide average air pollution and state-wide average prevalence of respiratory diseases); whereas in a cohort study the data pair exposure/health is known for each individual.
In spite of their weaknesses, ecological studies are useful because they can be carried out easily, quickly and inexpensively using data that are generally already available. If interesting and strong associations are observed, the results of ecological studies can provide the opportunity for later, more carefully designed studies (though more expensive and time-consuming) to build on the initial observations.
Cohort study
A cohort study or panel study is a form of longitudinal study used in medicine, social science, actuarial science, and ecology. It is an analysis of risk factors and follows a group of people who do not have the disease, and uses correlations to determine the absolute risk of subject contraction...
and case-control studies because it is susceptible to the ecological fallacy
Ecological fallacy
An ecological fallacy is a logical fallacy in the interpretation of statistical data in an ecological study, whereby inferences about the nature of specific individuals are based solely upon aggregate statistics collected for the group to which those individuals belong...
. An example of an ecological study is the analysis of the effects of disinfection byproducts on newborn babies, using 109 Massachusetts towns as units of analysis (Wright et al. 2004). (For an environmental definition of this term see Ecology
Ecology
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
.)
Ecological studies can be easily confused with cohort studies, especially if different cohorts are located in different places. The difference is that in the case of ecological studies there is no information available about the individual members of the populations compared (e.g. comparing several states based on state-wide average air pollution and state-wide average prevalence of respiratory diseases); whereas in a cohort study the data pair exposure/health is known for each individual.
In spite of their weaknesses, ecological studies are useful because they can be carried out easily, quickly and inexpensively using data that are generally already available. If interesting and strong associations are observed, the results of ecological studies can provide the opportunity for later, more carefully designed studies (though more expensive and time-consuming) to build on the initial observations.