Levels of evidence

In medicine, levels of evidence are arranged in a ranking system used in evidence-based practices to describe the strength of the results measured in a clinical trial or research study. The design of the study (such as a case report for an individual patient or a double-blinded randomized controlled trial) and the endpoints measured (such as survival or quality of life) affect the strength of the evidence.

Definition

The National Cancer Institute defines levels of evidence as "a ranking system used to describe the strength of the results measured in a clinical trial or research study. The design of the study [...] and the endpoints measured [...] affect the strength of the evidence."[1]

History

The term was first used in a 1979 report by the "Canadian Task Force on the Periodic Health Examination" to "grade the effectiveness of an intervention according to the quality of evidence obtained".[2]:1195 The task force used four levels:

The Canadian task force (CTF) graded their recommendations into a 5-point A–E scale: A: Good level of evidence for the recommendation to consider a condition, B: Fair level of evidence for the recommendation to consider a condition, C: Poor level of evidence for the recommendation to consider a condition, D: Fair level evidence for the recommendation to exclude the condition, and E: Good level of evidence for the recommendation to exclude condition from consideration.[2]:1195

The CTF updated their report in 1984,[3] in 1986[4] and 1987.[5]

The United States Preventive Services Task Force (USPSTF) came out with its guidelines (based on the CTF) in 1988.[6][7]

Over the years many more grading systems have been described.[8]

Another example of a system for grading evidence is the Oxford (UK) CEBM Levels of Evidence, Most of the evidence ranking schemes grade evidence for therapy and prevention, but not for diagnostic tests, prognostic markers, or harm. The Oxford CEBM Levels of Evidence addresses this issue and provides 'Levels' of evidence for claims about prognosis, diagnosis, treatment benefits, treatment harms, and screening. The original CEBM Levels was first released in September 2000 for Evidence-Based On Call to make the process of finding evidence feasible and its results explicit. As published in 2009[9] they are :

In 2011, the Oxford CEBM Levels were redesigned by an international team to make it more understandable and to take into account recent developments in evidence ranking schemes. The Oxford CEBM Levels of Evidence have been used by patients, clinicians and also to develop clinical guidelines including recommendations for the optimal use of phototherapy and topical therapy in psoriasis[10] and guidelines for the use of the BCLC staging system for diagnosing and monitoring hepatocellular carcinoma in Canada.[11]

Limitations

The hierarchy of evidence produced by a study design has been questioned, because guidelines have "failed to properly define key terms, weight the merits of certain non-randomized controlled trials, and employ a comprehensive list of study design limitations".[12]

See also

References

  1. ↑ National Cancer Institute (n.d.). "NCI Dictionary of Cancer Terms: Levels of evidence". US DHHS-National Institutes of Health. Retrieved 8 December 2014.
  2. 1 2 Canadian Task Force on the Periodic Health Examination. (3 November 1979). "Task Force Report: The periodic health examination." (PDF). Can Med Assoc J 121 (9): 1193–1254. PMC 1704686. PMID 115569. Retrieved 8 December 2014.
  3. ↑ Canadian Task Force on the Periodic Health Examination. (15 May 1984). "Task Force Report: The periodic health examination. 2. 1984 update". Can Med Assoc J 130 (10): 1278–1285. PMC 1483525. PMID 6722691. Retrieved 8 December 2014.
  4. ↑ Canadian Task Force on the Periodic Health Examination. (15 May 1986). "Task Force Report: The periodic health examination. 3. 1986 update". Can Med Assoc J 134 (10): 721–729.
  5. ↑ Canadian Task Force on the Periodic Health Examination. (1 April 1988). "Task Force Report: The periodic health examination. 2. 1987 update". Can Med Assoc J 257 (7): 618–26. PMC 1267740. PMID 3355931.
  6. ↑ Robert Lawrence; U. S. Preventive Services Task Force Edition (1989). Guide to Clinical Preventive Services. DIANE Publishing. ISBN 1568062974. Retrieved 9 December 2014.
  7. ↑ U.S. Preventive Services Task Force (August 1989). Guide to clinical preventive services: report of the U.S. Preventive Services Task Force. DIANE Publishing. pp. 24–. ISBN 978-1-56806-297-6.Appendix A
  8. ↑ Welsh, Judith (January 2010). "Levels of evidence and analyzing the literature". National Institutes of Health Library. Retrieved 9 September 2015.
  9. ↑ "Oxford Centre for Evidence-based Medicine – Levels of Evidence (March 2009)". Centre for Evidence-Based Medicine. Retrieved 25 March 2015.
  10. ↑ OCEBM Levels of Evidence Working Group. "The Oxford Levels of Evidence 2’".
  11. ↑ Paul, C.; Gallini A; Archier E; et al. (2012). "Evidence-Based Recommendations on Topical Treatment and Phototherapy of Psoriasis: Systematic Review and Expert Opinion of a Panel of Dermatologists". Journal of the European Academy of Dermatology and Venerology 26 (Suppl 3): 1–10. doi:10.1111/j.1468-3083.2012.04518.x. PMID 22512675.
  12. ↑ Gugiu, PC; Westine, CD; Coryn, CL; Hobson, KA (3 April 2012). "An application of a new evidence grading system to research on the chronic care model". Eval Health Prof. 36 (1): 3–43. doi:10.1177/0163278712436968. Retrieved 8 December 2014.

External links

 This article incorporates public domain material from the U.S. National Cancer Institute document "Dictionary of Cancer Terms".

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