What is the purpose of a control group in a study?

The purpose of a control group in a study is to provide a baseline for comparison against the experimental group. This allows researchers to assess the effects of the intervention or treatment being studied. By comparing outcomes between the control group, which does not receive the intervention, and the experimental group, which does, researchers can determine whether any observed effects are due to the intervention itself or other factors.

Control groups help ensure that the results are attributable to the treatment rather than external influences, such as time or subject differences. For instance, if an experimental group shows significant improvement after receiving a treatment, comparing it with a control group that has not received the treatment (and is otherwise identical) helps clarify whether the treatment was the cause of that improvement.

While observing long-term outcomes, enhancing external validity, and measuring effect size accurately are important aspects of research, they do not encapsulate the primary function of a control group. Instead, the control group’s key role is centered on establishing that baseline for evaluating the direct effects of the experimental intervention.