Which arrangement correctly places ASHA's levels of evidence in order from highest priority/most rigorous to lowest?

• A. A broad synthesis of literature (e.g., meta-analysis, systematic review); Well-designed randomized control trial; Correlational study; Expert opinion
• B. Correlational study; Expert opinion; A broad synthesis of literature (e.g., meta-analysis, systematic review); Well-designed randomized control trial
• C. A broad synthesis of literature (e.g., meta-analysis, systematic review); Well-designed randomized control trial; Correlational study; Expert opinion
• D. Well-designed randomized control trial; A broad synthesis of literature (e.g., meta-analysis, systematic review); Expert opinion; Correlational study

Answer: (C)

Think of evidence as a ladder where higher rungs combine more information and reduce bias. A broad synthesis of the literature—like a meta-analysis or systematic review—sits at the top because it pools multiple studies, weighs their quality, and provides an overall estimate of effect, giving a more reliable picture than any single study.

Just below that, a well-designed randomized controlled trial is valued for its internal validity. Random assignment and a control group help isolate the effect of the intervention and minimize confounding factors, making causal conclusions more trustworthy than observational findings.

Below that come correlational studies, which can reveal associations but can’t establish causation due to potential confounding factors and lack of randomization.

At the bottom sits expert opinion, which is based on experience or interpretation rather than new empirical data, and therefore considered the least strong form of evidence.

So the correct arrangement places a broad synthesis first, followed by a well-designed randomized trial, then correlational studies, and finally expert opinion.