Which of the following presents the correct order of Levels of Evidence from highest to lowest?

• A. 2a, 1a, 1b, 2b, 3a, 3b, 4, 5
• B. 1a, 1b, 2a, 2b, 3a, 3b, 4, 5
• C. 1a, 2a, 1b, 2b, 3a, 3b, 4, 5
• D. 1a, 1b, 2b, 2a, 3a, 3b, 4, 5

Answer: (B)

Levels of Evidence rank study designs by how much confidence they provide about a treatment effect. The strongest evidence comes from high-level syntheses and trials, and the strength decreases as designs become less rigorous or more prone to bias. A systematic review or meta-analysis of randomized trials sits at the top, and within that top tier, an individual randomized trial is considered stronger than nonrandomized studies. As you move down, well-designed nonrandomized studies are next, followed by observational designs, then case series, and finally expert opinion.

That gives the correct progression as: 1a, then 1b, then 2a, then 2b, then 3a, then 3b, then 4, then 5.