Table 1 Grading system for level of evidence
From: A multidisciplinary evidence-based guideline for minimally invasive surgery.
Level | Studies on therapy/prevention | Studies on diagnostic accuracy | Studies on harm, etiology or prognosis |
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A1 | Systematic review/meta-analysis of at least two independent studies of A2 level with consistent results | ||
A2 | Double-blind randomized controlled trial of good quality and sufficient power | Study with respect to a reference test (gold standard) with pre-defined cut-off values, among large series consecutive persons that received both the index and the reference test and adequate blinding of interpretation of test results | Prospective cohort study of sufficient power and follow-up, adequate control for confounding and selective follow up |
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B | Randomized controlled trial of modest quality or insufficient power, or other analytic study (e.g., case–control study, cohort study) | A comparison with a reference standard that does not meet the criteria required for level A2 evidence | Prospective cohort study that does not meet the criteria required for level A2 evidence. Or retrospective cohort study or case–control study |
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C | Non-analytic study | ||
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D | Expert opinion | ||
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Level | Conclusion based on | ||
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1 | One systematic review (A1) or at least two independent randomized controlled trials of level A2 | ||
2 | One study of level A2 or at least 2 independent studies of level B | ||
3 | One study of level B or C | ||
4 | Expert opinion | ||