The control group in an experiment does not receive a treatment or experimental condition. Researchers compare results from the experimental group with those of the control group to find an effect or statistically significant difference with the treatment.
Members of the control group must be similar to those in the treatment group in order to ensure that any differences are due to random chance or influence from the independent variable. To create similar groups, researchers randomly locate and assign participants to each group. Participants in both the control and treatment groups take the same pre-tests and post-tests. The treatment that those in the control group do not receive is the independent variable.