Table 3. Grades of recommendations according to quality of evidence*.

Grade A

Based on clinical studies of good quality and consistency with at least one randomized trial

Grade B

Based on well-designed studies (prospective, cohort) but without good randomized clinical trials

Grade C

Based on poorer quality studies (retrospective, case series, expert opinion)

*, modified from Oxford Centre for Evidence-Based Medicine (http://www.cebm.net/oxford-centre-evidence-based-medicine-levels-evidence-march-2009/).