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Table 1 Levels of evidence

From: Using the modified Delphi method to establish clinical consensus for the diagnosis and treatment of patients with rotator cuff pathology

1 Evidence obtained from:
• systematic review of randomized controlled trials;
• high-quality randomized controlled trials;
• high-quality prospective studies (e.g., all patients were enrolled at the same point of their disease with 80 % follow-up of enrolled patients); or
• testing of previously developed diagnostic criteria in series of consecutive patients.
2 Evidence obtained from:
• systematic review of level 2 studies or level 1 studies with inconsistent results;
• lesser quality randomized controlled trials (e.g., < 80 % follow-up, no blinding, or improper randomization);
• prospective comparative studies;
• retrospective studies;
• lesser quality prospective studies (e.g., patients enrolled at different points in their disease or <80 % follow-up); or
• development of diagnostic criteria on the basis of consecutive patients (with universally applied reference gold standard).
3 Evidence obtained from:
• systematic review of level 3 studies;
• case control studies;
• retrospective comparative studies; or
• study of nonconsecutive patients (without consistently applied reference gold standard).
4 Evidence obtained from:
• case series; or
• case control study with poor reference standard.
5 Evidence obtained from:
• expert opinion.