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 4 levels: I-Evidence from at least one randomized controlled trial, II1-Evidence from at least one well designed cohort or case control study, ie. a controlled trial which is not randomized and II2-Comparisons between times and places with or without the intervention and III-opinions of respected authorities, based on clinical experience, descriptive studies or reports of expert committees.
The task force 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 Canadian task force has 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 in 1988. [6] Over the years many more grading systems have been described.
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".[7]
The most recent levels of evidence is provided by the Centre for Evidence Based Medicine, Oxford:[8]
- 1a: Systematic reviews (with homogeneity) of randomized controlled trials
- 1b: Individual randomized controlled trials (with narrow confidence interval)
- 1c: All or none randomized controlled trials
- 2a: Systematic reviews (with homogeneity) of cohort studies
- 2b: Individual cohort study or low quality randomized controlled trials (e.g. <80% follow-up)
- 2c: "Outcomes" Research; ecological studies
- 3a: Systematic review (with homogeneity) of case-control studies
- 3b: Individual case-control study
- 4: Case-series (and poor quality cohort and case-control studies)
- 5: Expert opinion without explicit critical appraisal, or based on physiology, bench research or "first principles"
See also
References
- ↑ National Cancer Institute (n.d.). "NCI Dictionary of Cancer Terms: Levels of evidence". US DHHS-National Institutes of Health. Retrieved 8 December 2014.
- ↑ 2.0 2.1 Canadian Task Force on the Periodic Health Examination. (3 November 1979). "Task Force Report: The periodic health examination.". Can Med Assoc J 121 (9): 1193–1254. PMC 1704686. PMID 115569. Retrieved 8 December 2014.
- ↑ 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.
- ↑ 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.
- ↑ 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.
- ↑ Robert Lawrence; U. S. Preventive Services Task Force Edition (1989). Guide to Clinical Preventive Services. DIANE Publishing. ISBN 1568062974. Retrieved 9 December 2014.
- ↑ 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.
- ↑ "Oxford Centre for Evidence-based Medicine – Levels of Evidence (March 2009)". Centre for Evidence-Based Medicine. Retrieved 25 March 2015.
External links
- Evidence levels with explanations Entry in the Centre for Evidence Based Medicine
- Evidence based medicine resources page, with a diagram showing different levels of evidence forming a pyramid
This article incorporates public domain material from the U.S. National Cancer Institute document "Dictionary of Cancer Terms".