What Is Allocation Concealment?

Looking for the full method? Read the detailed guide: Randomized Controlled Trials Explained.

Allocation concealment is the practice of keeping the next participant's group assignment hidden from the people who enrol them, until the participant is irrevocably in the trial. It prevents selection bias in who is enrolled into which group.

Example

Invented for teaching: A central telephone or web system assigns each participant after enrolment is complete, so the recruiting clinician cannot predict or influence the assignment. Sealed, opaque, sequentially numbered envelopes are another method when properly used.

Common misunderstanding

Allocation concealment is not the same as blinding. Concealment applies before and during assignment and is always possible in randomised trials; blinding applies after assignment and is not always possible.

Learn more

See Randomized Controlled Trials Explained.

This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.