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Grades are provided for both quality of the evidence and strength of clinical recommendations. Key to Quality of Evidence and Strength of Clinical Recommendation Grading Quality of Evidence Levels Grade Study Type A • Meta-Analysis • Systematic Review • Randomized Clinical Trial • Diagnostic Studies (Grade A) ○ Do not have a narrow population ○ Do not use a poor reference standard ○ No case control studies of diseases or conditions B • Randomized Clinical Trial (weaker design) • Cohort Studies ○ Retrospective ○ Prospective • Diagnostic Studies (Grade B - only one of the following) ○ Narrow population ○ Sample used does not reflect the population to whom the test would apply ○ Uses a poor reference standard ○ Comparison between the test and reference standard is not blinded ○ Case control studies of diseases or conditions C • Case Control Studies ○ Study of sensitivity and specificity of a diagnostic test, population-based descriptive study of diseases or conditions ○ Retrospective or prospective • Diagnostic Studies (Grade C - at least two or more of the following) ○ Narrow population ○ Sample used does not reflect the population to whom the test would apply ○ Uses a poor reference standard ○ Comparison between the test and reference standard is not blinded • Studies of Strong Design ○ With substantial uncertainty about conclusions or serious doubts about generalizations, bias, research design, or sample size • Nonrandomized Trials D • Cross Sectional Studies • Case Reports/Series • Reviews • Position Papers • Expert Opinion • Reasoning from Principle 9 aoa.org Strength of Clinical Recommendation Levels Strong Recommendation:

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