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. Author manuscript; available in PMC: 2024 Feb 1.
Published in final edited form as: J Emerg Med. 2023 Apr 21;65(2):e71–e80. doi: 10.1016/j.jemermed.2023.04.012

Table 1.

Levels of Evidence and Strength of Recommendations

Level of Evidence Strength of Recommendation
Level I Level A
 Randomized, controlled trial or meta-analysis of randomized trials Generally accepted principles for patient care that reflect a high degree of clinical certainty (e.g., based on evidence from 1 or more Class of Evidence I or multiple Class of Evidence II studies).
Level II Level B
 Nonrandomized trial or retrospective Recommendations for patient care that may identify a particular strategy or range of strategies that reflect moderate clinical certainty (e.g., based on evidence from 1 or more Class of Evidence II studies or strong consensus of Class of Evidence III studies).
Level III Level C
 Case series Recommendations for patient care that are based on evidence from Class of Evidence III studies or, in the absence of adequate published literature, based on expert consensus.

Source: American College of Emergency Physicians (4).