Information from the control group allows the researchers to see whether the new treatment(s) are more or less effective than the current standard treatment.
The decision about which treatment each participant in a randomised controlled trial receives is made at random – based on chance, rather than decided by the doctor or participant. This process is called randomisation.
For example, if a doctor chose which treatment a patient should receive as part of a trial, she or he might give the new treatment to sicker patients, or to younger patients. This would make the results of a trial unreliable, as it could exaggerate or hide the effects of the treatment.
Randomised controlled trials are the most reliable way to compare treatments.