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
View who reviewed this content
View our editorial policy

Support services

Coping with cancer?
Speak to a health professional or to someone who has been there, or find a support group or forum

Need legal and financial assistance?
Pro bono services, financial and legal assistance, and no interest loans

Looking for transport, accommodation or home help?
Practical advice and support during and after treatment

Cancer information

What is cancer?
How cancer starts and spreads

Dealing with the diagnosis
Common reactions to a cancer diagnosis and how to find hope

View our publications
Guides and fact sheets for people with cancer, their families and friends