What is the purpose of randomization in a clinical trial?

• A. To ensure all participants receive the experimental treatment
• B. To bias the study toward desired outcomes
• C. To guarantee equal numbers in groups
• D. To assign participants randomly to groups to reduce bias

Answer: (D)

Random assignment of participants to groups reduces bias by making the groups comparable at the start. When allocation is left to chance, characteristics that could influence outcomes—like age, disease severity, and other health factors—tend to distribute evenly between the intervention and control groups. This balance means that differences in outcomes are more likely due to the treatment itself rather than preexisting differences, which supports valid conclusions about causality and allows proper use of statistical tests.

It’s not about ensuring everyone receives the experimental treatment, nor about steering results toward a desired outcome. It also doesn’t guarantee perfectly equal group sizes; randomization can produce uneven numbers, though researchers sometimes use methods to balance groups.