Ecological study

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 Harvard Six Cities Study which was part of evidence used for air pollution standards in the United States. (For an environmental definition of this term see Ecology.)