Clinical studies are the most reliable epidemiological studies because researchers have the greatest control of the data. In clinical studies, researcher study people exposed to a substance and compare them to groups of people who have no such exposure, i.e,. “control groups.” When it comes to chemicals, such as pharmaceuticals, clinical studies involve administering specific amounts of a drug to human volunteers under controlled conditions, observing the effects, then comparing results to a control group with no or significantly lower exposures. For example, a clinical drug trial might include assessing the health of carefully selected volunteers both before and after administering the drug. These results would then be compared to a similar group given a placebo.
Clinical trials to assess the danger of non-pharmaceutical chemicals are limited in scope because of the ethical issues associated with tests involving human subjects. Thus, human testing is limited to low-risk, low impact exposures, such as assessing the potential of skin irritations from bug repellants.
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