Table 4.

ACG Grading Recommendations and Levels of Evidence[2]

Grading Recommendations	Levels of Evidence
A Two or more level 1 trials without conflicting evidence from other level 1 trials	1 RCTs with P < .05, adequate sample size, appropriate methodology
B Single level 1 trial or 2 or more level 1 trials with conflicting evidence from other level 1 trials or 2 or more level 2 trials	2 RCTs with P > .05 or inadequate sample size and/or inappropriate methodology
C Based on evidence from levels 3 to 5	3 Non-RCTs with contemporaneous controls 4 Non-RCTs with historical controls 5 Case series

RCT = randomized controlled trial