What is the main reason for using a control group in experiments?

Using a control group in experiments is primarily intended to provide a comparison for evaluating the effects of the treatment. By having a control group that does not receive the intervention, researchers can isolate the impact of the treatment itself from other factors that might influence the outcome. This allows for a clearer understanding of whether the changes observed in the experimental group can be attributed to the treatment or if they might have occurred due to other variables.

The control group serves as a baseline that helps to assess the effectiveness of the treatment being tested. If the treatment group shows significant changes while the control group does not, researchers can be more confident that the treatment had a genuine effect. This approach is fundamental in establishing cause-and-effect relationships within experimental research.

In contrast, increasing sample size, ensuring random selection, and testing all variables are important aspects of study design but do not directly address the need for comparison to understand the effects of the treatment. Thus, the primary justification for including a control group revolves around enabling this essential comparison to discern the true impact of the intervention being tested.