Epidemiology is the study of the occurrence of disease in groups of people, and the use of that information to control health problems. Epidemiological studies look at large numbers of people (a population, not just an individual). This is done to study the association between exposure to a substance or event with the occurrence of an identified disease. Most health regulations today are based on epidemiological studies.
There are some complications with epidemiological studies. Many detailed factors about substance exposure, including the length of exposure and intensity of exposure, can affect study results. According to the National Institute of Environmental Health Sciences, this information may not be available or reliable because:
People may not know what they have been exposed to or the amount of their exposure.
People find it very difficult to recall details of exposures that happened many years ago.
In an epidemiological study, it can be difficult to find small differences in the rates of common diseases with precision. When a very large number of people may be reliably affected by a common disease, relatively small differences cannot be identified by epidemiological studies.
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