How does randomization work in a clinical trial?

Randomization is the process researchers use to assign clinical trial participants by chance to different study groups. In most cases, a computer program does the assigning, rather than a doctor or the participant deciding.

In the simplest trial design, there are two groups: an investigational group, which receives the study intervention or drug being tested, and a control group, which receives the standard treatment already used for that cancer.

Randomization is used mostly in later-phase trials, especially phase 3, when researchers are comparing a new treatment head-to-head against the current standard of care.

The reason researchers randomize is to prevent bias. If doctors chose who went into each group, they might unintentionally place healthier patients into the treatment group, making that treatment look more effective than it really is. By assigning people by chance, researchers make it more likely that any difference in outcomes between groups reflects the treatment itself, not differences among the people receiving it.