What are common randomization methods and their purpose?

• A. Simple randomization alone.
• B. Block randomization only to balance group sizes.
• C. Simple randomization; block randomization to balance group sizes; stratified randomization to balance on key prognostic factors.
• D. Randomization methods are only used in blinded trials.

Answer: (C)

Randomization methods are used to create comparable groups and minimize bias in a trial. Simple randomization gives each participant an equal chance of assignment, which works well in large studies but can lead to imbalanced group sizes or uneven distribution of important prognostic factors in smaller trials. Block randomization keeps group sizes more equal as enrollment progresses, preventing one arm from becoming much larger than the other. Stratified randomization goes further by grouping participants on key prognostic factors (such as disease severity or age) and randomizing within those groups, ensuring those factors are evenly distributed across treatment arms. Together, these methods address both balance in numbers and balance of important characteristics, improving comparability and statistical power. Randomization is used beyond blinded trials as well, to reduce bias and confounding in various trial designs.