A controlled experiment is a scientific test done under controlled conditions, meaning that just one (or a few) factors are changed at a time, while all others are kept constant. The purpose of a controlled experiment is to minimize the effects of variables other than the independent variable, which increases the reliability of the results. Controlled experiments require a control group that receives a standard treatment, a fake treatment, or no treatment. The control group serves as a comparison group to the experimental group, which receives the treatment or manipulation. By comparing the outcome of the control group with the experimental group, researchers can assess whether it’s the treatment specifically that caused the outcomes, or whether time or any other treatment might have resulted in the same effects.

Controlled experiments are a part of the scientific method and are used to test hypotheses. They eliminate alternate explanations of experimental results, especially experimental errors and experimenter bias. Many controls are specific to the type of experiment being performed, and the selection and use of proper controls to ensure that experimental results are valid can be very difficult. Controlled experiments have disadvantages when it comes to external validity, which is the extent to which the results can be generalized to broad populations and settings. The more controlled the experiment is, the less it resembles real-world contexts, making it harder to apply the findings outside of a controlled setting.