Clinical trials are a type of epidemiologic study typically used to test the efficacy of a medical treatment on a group of human study subjects. Clinical trials are forward-going or prospective in nature and allow researchers a higher degree of control over exposures and confounding risk factors among study subjects than other type of epidemiologic studies (e.g,. case-control and cohort).
As a conceptual example, researchers want to test whether a treatment, like a new drug, cures a disease. So the researchers identify 1,000 subjects with the disease and treat half of them with the drug and the other half with a placebo. The efficacy of the drug is evaluated at the end of the trial period by comparing the incidence of disease among subjects taking the drug as compared to subjects taking the placebo.
Roughly speaking, if the comparison ratio (termed a “relative risk” for ease of discussion) is less than 1.0, then the drug is statistically associated (correlated) with successful treatment of the disease. If the relative risk is equal to 1.0, then there is no statistical difference between the drug and the placebo. If the relative risk is greater than 1.0, then drug is statistically associated with a worsening of the disease. Keep in mind that the interpretation of relative risks is subjective in nature. This is discussed in greater detail later.
It’s important to keep in mind that the clinical trial can only statistically associate (correlate) the treatment with an effect on the disease. A clinical trial, by itself, cannot prove a cause-and-effect relationship. This is because, like all epidemiologic studies, clinical trials are entirely statistical in nature. That is, the researchers are simply counting the number of study subjects with and without disease at the beginning and end of the study and then comparing those counts according to which which study subjects did and did not receive the treatment.
Evaluate a clinical trial?