Researchers use controlled studies to determine the efficacy of things such as products, drugs, advertising campaigns, etc. In the studies they limit subjects’ exposure to outside influences such as their diets if a weight-loss drug is being evaluated.
On the other side of the coin are random studies, where people are given a drug, for example, but maintain their normal lives.
In determining the effectiveness of the vaccines to treat COVID-19, the U.S. prison system is unwittingly serving as something of a controlled study.
