Guidelines to diagnose and treat peri-levator high-5 anal fistulas: Supralevator, suprasphincteric, extrasphincteric, high outersphincteric, and high intrarectal fistulas

Table 1 Levels of evidence for therapeutic studies[49]

Level		Type of evidence
1	A	Systematic review (with homogeneity) of RCTs
	B	Individual RCT (with narrow confidence intervals)
	C	All or none study
2	A	Systematic review (with homogeneity) of cohort studies
	B	Individual Cohort study (including low quality RCT, e.g., < 80% follow-up)
	C	“Outcomes” research; Ecological studies
3	A	Systematic review (with homogeneity) of case-control studies
	B	Individual Case-control study
4		Case series (and poor-quality cohort and case-control study
5		Expert opinion without explicit critical appraisal or based on physiology bench research or “first principles”

Citation: CEBM. OCEBM levels of evidence. [cited 11 January 2022]. Available from: https://www.cebm.ox.ac.uk/resources/levels-of-evidence/ocebm-levels-of-evidence. Copyright© 2022 University of Oxford.

RCTs: Randomized controlled trials.