Table 1.

Level of Evidence based on Oxford criteria 2009 [18].

LoE		Study Type
I	a	Meta analysis/systematic review of studies with LoE Ib
	b	“randomized controlled clinical trial” (RCT)
II	a	Meta analysis/systematic review of studies with LoE IIb
	b	“controlled clinical trial” (CCT)/comparative prospective cohort study (with control group)
III	a	Meta analysis/systematic review of studies with LoE IIIb
	b	Retrospective cohort study/case-control study
IV		Non-controlled observational study > 1 patient (e.g., case series), studies other than in vivo studies of human subjects (e.g., animal experiment, cadaver study), consensus paper
V		Case study, non-systematic secondary literature, expert opinion