Observational epidemiological studies are classified as ecological, case—control, or cohort.
In ecologic epidemiological studies, data on populations, rather than data on individuals, are compared. An example of an ecologic study is the evaluation of geographic areas with high-background radiation levels compared with areas with “normal” background levels. Ecological studies aggregate data over a population in a particular area. Ecological studies are subject to problems of correlations between aggregated disease rates and aggregated measures of exposure. Ecological studies compare average exposure with average cancer risk. Advantages of ecological studies are: (1) they are easy and inexpensive; (2) they can document the frequency of disease over time; and (3) they usually include a large population. A good ecological study adequately controls for confounding factors, and has geographic areas with adequate numbers of dose measurement, small variability of dose within individual geographic regions relative to variability in other regions, availability of high-quality health data across geographic regions, and relatively stable populations [7].
Cohort and case—control studies use data for individuals. Case—control studies compare radiation exposure in individuals with cancer and without cancer. In case—control studies, individuals with a specific cancer are compared with a control group of individuals without the cancer with respect to their past exposure to radiation. Case—control studies are usually not used in radiation epidemiology, with the exception for studies of indoor radon and lung cancer. Case—control studies are susceptible to biases of appropriate selection of controls and valid retrospective determination of dose [7].
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(2010). Biased Epidemiological Studies. In: Sanders, C.L. (eds) Radiation Hormesis and the Linear-No-Threshold Assumption. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-642-03720-7_7
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