Controlled experiments are important because they let the experimenter eliminate uncertainty during an experiment, ensuring the results are trustworthy. In a controlled experiment, every variable except the one being tested is held constant, which eliminates the possibility that the results are due to an uncontrolled factor.
In a controlled experiment, the researcher creates two separate groups, the control group and the experimental group. The control group is not given the treatment or drug, while the experimental group is. This type of setup allows the researcher to measure the difference in responses between the two groups, which makes it easy to tell if the experimental treatment caused the observed results.
A type of controlled experiment called a double-blind randomized experiment, in which participants are assigned to a control group or a test group without knowing which individuals are in which group, is considered the most rigorous and reliable way of testing new treatments or medications.
In some cases, such as experiments dealing with human patients, completely controlled experiments aren't truly possible since the participants are not biologically identical. However, scientists typically try to control as many variables as possible in clinical trials involving humans. They also use large groups of study participants to control for other factors that might potentially affect the results.