Which feature primarily differentiates a randomized controlled trial from an observational cohort study?

Which feature primarily differentiates a randomized controlled trial from an observational cohort study?

• A. Use of a control group
• B. Randomization to reduce confounding
• C. Blinding of participants and researchers
• D. Large sample size

Answer: (B)

The feature that distinguishes a randomized trial from an observational cohort study is randomization to assign participants to the intervention or control group. Random assignment makes the groups comparable on both known and unknown factors, so differences in outcomes can be attributed more confidently to the intervention itself rather than to preexisting differences between participants. This balancing of confounders—measured and unmeasured—is what enables stronger causal interpretations in randomized trials. Having a control group is common to both designs, but in observational studies the assignment to exposure isn’t random and outcomes can be influenced by confounding factors that differ between exposed and unexposed groups. Blinding can occur in randomized trials but isn’t mandatory and isn’t the defining feature. Large sample size can occur in either design and doesn’t by itself separate randomized trials from observational studies.

The feature that distinguishes a randomized trial from an observational cohort study is randomization to assign participants to the intervention or control group. Random assignment makes the groups comparable on both known and unknown factors, so differences in outcomes can be attributed more confidently to the intervention itself rather than to preexisting differences between participants. This balancing of confounders—measured and unmeasured—is what enables stronger causal interpretations in randomized trials.

Having a control group is common to both designs, but in observational studies the assignment to exposure isn’t random and outcomes can be influenced by confounding factors that differ between exposed and unexposed groups. Blinding can occur in randomized trials but isn’t mandatory and isn’t the defining feature. Large sample size can occur in either design and doesn’t by itself separate randomized trials from observational studies.