Randomization in clinical trials: how it works

What randomization means

Randomization means a computer assigns you to a study group by chance, like flipping a coin.

Neither you nor your doctor chooses which group you're in. Groups might get the new treatment, the standard treatment or a placebo.

Why it matters

Randomization makes the groups as similar as possible, so differences in results are more likely caused by the treatment itself.

Without it, researchers might unconsciously put healthier people in one group, which could make a treatment look better or worse than it really is.

How groups are split

Many studies split people evenly between groups, but some put more people in the new-treatment group.

For example, a 2:1 study puts two people in the treatment group for every one in the comparison group. The consent form tells you your chances.

Blinding, explained simply

Blinding means you don't know which group you're in, so expectations don't affect the results.

In a single-blind study, you don't know. In a double-blind study, neither you nor the study team knows. An open-label study tells everyone which treatment is being given.

Your safety while blinded

In an emergency, the study team can find out which treatment you received. Being blinded doesn't change how closely your health is monitored, and you can leave the study at any time.

Questions to ask

Is this study randomized? What groups are there, and what are my chances of each? Is it blinded? Will I find out which group I was in after the study ends?

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Quick answers

What does randomization mean in a clinical trial?

Randomization means a computer assigns you to a study group by chance, like flipping a coin.

Why are clinical trials randomized?

Randomization makes the groups as similar as possible, so differences in results are more likely caused by the treatment itself.

Are study groups always the same size?

Many studies split people evenly between groups, but some put more people in the new-treatment group.

What is blinding in a clinical trial?

Blinding means you don't know which group you're in, so expectations don't affect the results.

Sources

• NIH — Clinical Research Trials and You: The Basics
• ClinicalTrials.gov — Learn About Studies