Randomization
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The process of assigning trial subjects to treatment or control groups by chance, to minimize selection bias and confounding so that observed differences in outcome can be attributed to the intervention rather than to systematic differences between groups. The randomization method and its concealment are pre-specified in the protocol and statistical analysis plan.
Common designs include simple randomization, block randomization (which keeps group sizes balanced over time), and stratified randomization (which balances known prognostic factors such as disease severity or site). The chosen method is fixed in advance and justified against the trial’s size and design.
Allocation concealment — keeping the randomization sequence unknown to those enrolling subjects until the moment of assignment — is a distinct safeguard from blinding: it prevents selection bias at enrollment, whereas blinding prevents assessment bias after enrollment.
The randomization code is held securely, usually by an independent party or an interactive response system, with a defined emergency-unblinding procedure so an individual subject’s treatment can be revealed quickly if their safety requires it.
- —Distinct from blinding: randomization controls group assignment, blinding controls who knows the assignment.
- —Allocation concealment prevents selection bias at the point of enrollment.
- —Common designs include simple, block, and stratified randomization to balance known prognostic factors.
- —The randomization code is held securely, with a defined emergency-unblinding procedure for participant safety.
ICH E9 Statistical Principles for Clinical Trials; ICH E10 Choice of Control Group and Related Issues in Clinical Trials; ICH E6(R3) GCP
Frequently asked questions
What is Randomization?
The process of assigning trial subjects to treatment or control groups by chance, to minimize selection bias and confounding so that observed differences in outcome can be attributed to the intervention rather than to systematic differences between groups. The randomization method and its concealment are pre-specified in the protocol and statistical analysis plan.
Which regulations cover Randomization?
ICH E9 Statistical Principles for Clinical Trials; ICH E10 Choice of Control Group and Related Issues in Clinical Trials; ICH E6(R3) GCP