In most trials, patients are divided into groups. One group will have the standard treatment used for their type of cancer. The other group will have the treatment being investigated in the trial. The results are compared to see which treatments are better or worse and what the side effects are.

When there is no standard treatment available, one of the groups is given a placebo instead of a treatment. This is an inactive treatment that looks like a real one.

To decide who is assigned to which group in a fair way, a computer places patients in treatment groups. This is called randomization.

You cannot know which treatment group you are in. In some trials, neither the patient nor the doctor knows which treatment the patient is receiving.