Randomised control trials

Randomised controlled trials (RCT) are the best way to test if a new treatment is effective. This is because they help prevent bias. Bias occurs when the results of a trial are influenced by human choice or other factors not related to the treatment being tested.

Most Phase 3 trials and some Phase 2 trials are randomised. In an RCT participants are randomly assigned into two groups, or arms, of the study, and the results of both groups are compared.

Test or experimental group (or arm) – This is the group that is given the experimental treatment being studied.

Control group (or arm) – This group receives the current best available standard treatment for the disease.

When randomly allocated groups are compared with each other, it is possible to reliably work out which treatment is better. This is because researchers can be certain that the results are related to the treatment or chance, and not to any other factors.


This information was last reviewed in May 2015
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