What is the role of randomization in a clinical trial?

• A. It is the preferred means of assuring comparability of test groups and minimizing selection bias.
• B. It guarantees that all confounders are controlled.
• C. It replaces the need for blinding.
• D. It is used only in parallel-group trials.

Answer: (A)

Randomization assigns participants to treatment groups by chance, so the groups are, on average, similar in prognosis and baseline characteristics. This equalizes known and unknown factors that could affect outcomes, which is what minimizes selection bias and helps ensure the groups are comparable before the intervention starts. Because the assignment isn’t influenced by investigators or participants, systematic differences are less likely to creep in through how people are chosen or allocated.

It’s important to remember that randomization does not guarantee control of all confounders. Imbalances can still occur by chance, especially in smaller trials. That’s why it’s also important to use allocation concealment and, when appropriate, blinding to further reduce bias.

Finally, randomization isn’t limited to parallel-group trials; it is used in other designs (like crossover or factorial trials) as well, to preserve the integrity of comparisons.