UK Community Advisory Board (UK-CAB)

Clinical trials – a guide for CAB members (page 8)

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  • Researchers assign participants to a medicine group “at random.” The researchers do not assign the volunteers to Group A (the control group, who will receive standard medication known to be safe and effective) or Group B (the investigational group, who will receive the new medicine being studied). Instead, a computer assigns each volunteer to a group by a process called “randomisation,” which is like flipping a coin: Heads = Group A, Tails = Group B.
  • This picture shows how randomisation works. All of the eligible volunteers are shown in the large group on the left. The computer assigns some of the participants to Group B, the “investigational group”. It assigns the others to Group A, the “control group”—the group receiving standard medicine known to be safe and effective.
  • If there is no medicine known to be safe and effective for the disease being studied, then the researchers may compare the new medicine with a “placebo,” which is a “dummy” pill that contains no medicine. For example, there is no medicine that is known to prevent tuberculosis in infants exposed to HIV infection at birth. In a clinical trial to test whether a new medicine can prevent HIV-exposed and infected infants from developing tuberculosis, researchers would test the medicine against a placebo.
  • Often researchers do not use a placebo if there is a medication in use that is safe and effective, such as medicine for HIV infection—they compare the new treatment to the one known to be effective.