Levels of evidence are used to guide the reader as to the strength of each individual recommendation. While there are many documented approaches to grading levels of evidence in clinical practice guidelines, we employed a broader system to rank evidence that also emphasizes the strength of meta-analyses or large, high-quality studies that may not involve interventions. In our grading system, Level A is the strongest level of evidence.
LEVEL A - Recommendation supported by at least 1 meta-analysis, systematic review, or randomized controlled trial of appropriate size with relevant control group.
LEVEL B - Recommendation supported by cohort studies that at minimum have a comparison group, well-designed single subject experimental designs, or small sample size randomized controlled trials.
LEVEL C - Recommendation supported primarily by expert opinion based on their experience, though uncontrolled case series without comparison groups that support the recommendations are also classified here.