Table 4.6

NHLBI Evidence Grading System

Evidence Quality Grading and Recommendation Strength
Evidence Quality for Each ESStrength of Each Recommendation
HighA – Strong
• Well-designed and conducted RCTsB – Moderate
ModerateC – Weak
• RCTs with minor limitationsD – Against
• Well-conducted observational studiesE – Expert Opinion
N – No Recommendation
Low
• RCTs with major limitations
• Observational studies with major limitations

Reproduced from Smith (19).

ES indicates evidence statement; NHLBI, National Heart, Lung, and Blood Institute; and RCTs, randomized controlled trials.