Intended for healthcare professionals

Analysis Rating quality of evidence and strength of recommendations

What is “quality of evidence” and why is it important to clinicians?

BMJ 2008; 336 doi: (Published 01 May 2008) Cite this as: BMJ 2008;336:995
  1. Gordon H Guyatt, professor1,
  2. Andrew D Oxman, researcher2,
  3. Regina Kunz, associate professor3,
  4. Gunn E Vist, researcher2,
  5. Yngve Falck-Ytter, assistant professor4,
  6. Holger J Schünemann, associate professor5
  7. for the GRADE Working Group
  1. 1Department of Clinical Epidemiology and Biostatistics, McMaster University, Hamilton, ON, Canada L8N 3Z5
  2. 2Norwegian Knowledge Centre for the Health Services, PO Box 7004, St Olavs plass, 0130 Oslo, Norway
  3. 3Basel Institute of Clinical Epidemiology, University Hospital Basel, Hebelstrasse 10, 4031 Basel, Switzerland
  4. 4Division of Gastroenterology, Case Medical Center, Case Western Reserve University, Cleveland, OH 44106, USA
  5. 5Department of Epidemiology, CLARITY Research Group, Italian National Cancer Institute Regina Elena, Rome, Italy
  1. Correspondence to: G H Guyatt, CLARITY Research Group, Department of Clinical Epidemiology & Biostatistics, Room 2C12, 1200 Main Street West Hamilton, ON, Canada L8N 3Z5 guyatt{at}

Guideline developers use a bewildering variety of systems to rate the quality of the evidence underlying their recommendations. Some are facile, some confused, and others sophisticated but complex

In 2004 the Grading of Recommendations Assessment, Development and Evaluation (GRADE) Working Group presented its initial proposal for patient management.1 In this second of a series of five articles focusing on the GRADE approach to developing and presenting recommendations we show how GRADE has built on previous systems to create a highly structured, transparent, and informative system for rating quality of evidence.

Summary points

  • A guideline’s formulation should include a clear question with specification of all outcomes of importance to patients

  • GRADE offers four levels of evidence quality: high, moderate, low, and very low

  • Randomised trials begin as high quality evidence and observational studies as low quality evidence

  • Quality may be downgraded as a result of limitations in study design or implementation, imprecision of estimates (wide confidence intervals), variability in results, indirectness of evidence, or publication bias

  • Quality may be upgraded because of a very large magnitude of effect, a dose-response gradient, and if all plausible biases would reduce an apparent treatment effect

  • Critical outcomes determine the overall quality of evidence

  • Evidence profiles provide simple, transparent summaries

A guideline’s formulation should include a clear question

Any question addressing clinical management has four components: patients, an intervention, a comparison, and the outcomes of interest.2 For example, consider the following: in patients with pancreatic carcinoma undergoing surgery what is the impact of a modified resection that preserves the pylorus compared with a standard wide tumour resection—variations of the Whipple procedure—on short term and long term mortality, blood transfusions, bile leaks, hospital stay, and problems with gastric emptying?

Perhaps the most common error in formulating the question is a failure to include all the outcomes that are of importance to patients.3 Critics …

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