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Table 1 Overview of a simplified and traditional hierarchy for grading the quality of evidence and strength of recommendations

From: Evidence-based medicine: Classifying the evidence from clinical trials – the need to consider other dimensions

Levels of Evidence

   Level I

Well conducted, suitably powered RCT

   Level II

Well conducted, but small and under-powered RCT

   Level III

Non-randomized observational studies

   Level IV

Non-randomized study with historical controls

   Level V

Case series without controls

Grades of recommendations

   Grade A

Level I

   Grade B

Level II

   Grade C

Level III or lower

  1. Levels of evidence are for an individual research investigation. Grading of recommendations is based on levels of evidence. Adapted from [1,2]. RCT, randomized controlled trial.
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Critical Care

ISSN: 1364-8535