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Table 1 Levels of evidence [6]

From: Methotrexate in juvenile idiopathic arthritis: advice and recommendations from the MARAJIA expert consensus meeting

Levels of evidence
1 Systematic review of all relevant randomized clinical trials or n-of-1 trials
2 Randomized trial or observational study with dramatic effect
3 Non-randomized controlled cohort/follow-up study (observational)
4 Case series, case-control study, or historically controlled study
5 Mechanism-based reasoning (expert opinion, based on physiology, animal or laboratory studies)
Grades of recommendation
A Consistent level 1 studies
B Consistent level 2 or 3 studies, or extrapolations from level 1 studies
C Level 4 studies, or extrapolations from level 2 or 3 studies
D Level 5 evidence or troubling, inconsistent or inconclusive studies of any level