What type of study is considered the highest level of evidence?

• A. Randomized controlled trials
• B. Expert opinion
• C. Narrative reviews
• D. Case reports

Answer: (A)

The strongest evidence comes from randomized controlled trials because random assignment helps balance known and unknown confounders, and a control condition allows you to attribute observed effects to the intervention rather than to other factors. When participants are randomly allocated to receive the treatment or a comparison (like placebo), and the study is properly powered and often blinded, biases are minimized and causal inferences are more credible.

Other options don’t offer the same level of rigor. Expert opinion reflects individual judgment and can be biased; narrative reviews may lack systematic methods and may overlook conflicting data; case reports describe single instances without controls, so they can’t establish causality or generalize to broader populations. Among these choices, the randomized controlled trial provides the strongest evidence for efficacy.