Epidemiology is the study of the occurrence of disease in people, and applying that information from the study to the control of health problems. Epidemiological studies look at the association of exposure to a substance or event with a large number of people who have an identified disease.
Most health regulations today are based on epidemiological studies. It is the most common method of determining the cause of a disease, and is a technique that is easily accepted and easily understood.
There are some complications with epidemiology. It is critical to know about exposure, quantity, and other details in order to produce a good epidemiological study. According to the National Institute of Environmental Health Sciences (NIEH), this information may not be available 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 occurred many years ago.
Also, epidemiology cannot detect small differences in the rates of common diseases. Although a very large number of people may be affected by a common disease, relatively small differences cannot be identified by epidemiology.
And, the NIEH states:
Epidemiology is entirely an after-the-fact science, that is, disease can be related to cause only after people have experienced exposures of sufficient intensity and duration to produce illness and death. Sometimes an entire generation is exposed to a chemical before epidemiological studies can prove that a particular compound does cause cancer or some other chronic disease.