Table 1.

Level of evidence modified from the Oxford Center of Evidence Based Medicine (OCEBM)⁹⁶

LEVEL OF EVIDENCE	STUDY CHARACTERISTICS
I	Evidence obtained from high-quality randomized controlled trials, prospective studies, or diagnostic studies.
II	Evidence obtained from lesser quality randomized control trials, prospective studies or diagnostic studies (e.g., improper randomization, no blinding, <80% follow-up)
III	Case controlled studies or retrospective studies.
IV	Case Series
V	Expert Opinion