Table 1. Level of evidence.

Level	Type of evidence
I	RCTs, or overwhelming evidence from observational studies
II	RCTs with important limitations, or exceptionally strong evidence from observational studies
III	Observational studies, or RCTs with notable limitations
IV	Clinical experience and observations, observational studies with important limitations, or RCTs with several major limitations
V	No evidence or difficult to analysis or based on expert opinion

RCT, randomized controlled trial.