Table 1.

Oxford Centre for Evidence-Based Medicine (OCEBM) Levels of Evidence.

Level	Levels of Evidence	Qty of Articles
1	Systematic reviews of randomised trials or n − 1 trials	N/A
2	Randomised trial or observation study with dramatic effect	21
3	Non-randomised controlled cohort/follow-up study	0
4	Case series, case-control studies, or historically controlled studies	4
5	Mechanism-based reasoning	0