What Is a Control Group?
Looking for the full method? Read the detailed guide: Randomized Controlled Trials Explained.
A control group is a group of participants who do not receive the test intervention and are used for comparison, so that the effect of the intervention can be judged. The control may receive a placebo, usual care or no treatment, depending on the question and ethics.
Example
Invented for teaching: In a trial of a new inhaler technique programme, the intervention group receives the programme and the control group receives usual care. Outcomes are compared between the groups.
Common misunderstanding
A control group is not the same as having a "baseline" before treatment in the same people. Also, a control group in an observational study is not randomly assigned, so it may differ from the exposed group in other ways.
Learn more
See Randomized Controlled Trials Explained.
References and further reading
- Schulz KF, Altman DG, Moher D; CONSORT Group. CONSORT 2010 statement: updated guidelines for reporting parallel group randomised trials. BMJ. 2010;340:c332. doi:10.1136/bmj.c332
- Hulley SB, Cummings SR, Browner WS, Grady D, Newman TB. Designing Clinical Research. 4th ed. Lippincott Williams & Wilkins; 2013. Link
Related reading
This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.