Level 1 | ∙ Randomised controlled trials with Low risk of bias as assessed by RoB 2.0 |
Level 2 | ∙ Randomised controlled trials with Some concerns or High risk of bias as assessed by RoB 2.0 ∙ Non-randomised controlled trials (including case–control, prospective and retrospective cohort studies) with Low or Moderate risk of bias as assessed by ROBINS-I |
Level 3 | ∙ Non-randomised controlled trials (including case–control, prospective and retrospective cohort studies) with Serious or Critical risk of bias as assessed by ROBINS-I ∙ Pre-post studies (any Downs and Black score) |
Level 4 | ∙ Case series defined by 3–5 individuals only (any Downs and Black score) ∙ Case report defined by 1–2 individuals only (any Downs and Black score) ∙ Cross-sectional controlled study (any Downs and Black score) |