What is the primary advantage of a randomized controlled trial over observational designs?

• A. RCTs require fewer participants.
• B. RCTs are always less expensive.
• C. Randomization minimizes confounding by evenly distributing known and unknown confounders.
• D. RCTs eliminate all biases.

Answer: (C)

Randomization puts participants into groups by chance, which makes the groups comparable in both measured and unmeasured characteristics. Because of this, differences in outcomes are more likely due to the intervention itself rather than preexisting differences between participants. In observational designs, treatment assignment often depends on patient or clinician choices, leading to systematic differences that confound the results. By evenly distributing known and unknown confounders, a randomized design strengthens causal inference and reduces bias from confounding. Of course, other biases can still occur, but the key advantage is the ability to isolate the effect of the intervention through random allocation.