Which feature most directly reduces confounding in a randomized trial?

Which feature most directly reduces confounding in a randomized trial?

• A. Larger sample size
• B. Blinding of participants and staff
• C. Placebo control
• D. Randomization of assignment to groups

Answer: (D)

Randomization directly creates comparable groups by chance, so both known and unknown confounders are balanced across the intervention and control groups. This balance makes it much more likely that any difference in outcomes is due to the intervention itself, not to other factors that could influence both treatment assignment and the outcome. Larger sample size improves precision and reduces random error, but it doesn’t guarantee that confounders are balanced. Placebo control helps manage expectancy effects, not the underlying distribution of confounders. Blinding reduces biases in measurement and behavior, but it doesn’t ensure that groups are balanced on confounding variables.

Randomization directly creates comparable groups by chance, so both known and unknown confounders are balanced across the intervention and control groups. This balance makes it much more likely that any difference in outcomes is due to the intervention itself, not to other factors that could influence both treatment assignment and the outcome.

Larger sample size improves precision and reduces random error, but it doesn’t guarantee that confounders are balanced. Placebo control helps manage expectancy effects, not the underlying distribution of confounders. Blinding reduces biases in measurement and behavior, but it doesn’t ensure that groups are balanced on confounding variables.