Evidence based medicine

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At its best, the evidence based medicine process is invoked to inform decisions, not to make them.


QuotationMarkLeft.png Evidence based medicine is the conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients. The practice of evidence based medicine means integrating individual clinical expertise with the best available external clinical evidence from systematic research. QuotationMarkRight.pngSackett DL et al.

It is perhaps best seen as a system supporting the application of the scientific method to clinical practice, and so its strengths and weaknesses extend as far back as any application of the scientific method to a problem in Medicine.

The current codified approach is primarily due to Professor A. Cochrane and this has resulted in much more effective dissemination and application of medical knowledge to the benefit of the individual patient. To fully understand the approach and its limitations requires not only an understanding of the scientific method, causality, and critical appraisal but wider philosophy around inductive, deductive, retroductive and abductive reasoning. Like all science, the approach can be misused and misrepresented, but has probably resulted in more mortality and morbidity benefits to the population of most Western nations in the last decade than any other factor.


Levels of Evidence

Several systems exist to systematise ways to rank levels of evidence or grades of recommendation based upon them[1][2][3]. A major problem is that these systems are multi-dimensional. Another is that in terms of clinical application the grading system is only as good as the respect that those applying it hold of those using it. Few can be bothered or have the ability to double check the original references that a guideline body for example used in reaching its grading conclusions[4]. It is unlikely that an American physician will respect guidelines from an European professional body as much as from an American one and this has led to inconsistencies in the management of say VTE and syncope which probably have real impact at a population level in terms of resources used relative to net health outcome.

Ways to indicate Levels of Evidence in Ganfyd articles

A set of templates has been developed that will produce in line text indicating the level of evidence. The expectation is that if you use these templates you will reference an external (web) reference in each case. Examples of how you might do so are given in the table. The templates have the ability to self reference a standard URL but this has been depreciated as since the templates were first developed Ganfyd has adopted the Vancouver style of referencing where-ever possible. (see talk for more details). Accordingly using the template like {{subst:CE B}} is regarded as most beneficial now !

Clinical Evidence Templates Example Table
Style You Copy and Paste You Get
Clinical Evidence {{subst:CE B|http://www.clinicalevidence.com/ceweb/about/guide.jsp}} beneficial
{{subst:CE_L}}<ref>http://www.clinicalevidence.com/ceweb/about/guide.jsp</ref> likely to be beneficial[5]
{{subst:CE T}} trade off between benefits and harms
{{subst:CE Q}} unknown effectiveness
{{subst:CE U}} unlikely to be benefical
{{subst:CE H}} likely to be ineffective or harmful
SORT {{subst:SORT A|http://http://www.aafp.org/afp/20040201/548.html}} A grade recommendation
{{subst:SORT B}}<ref>http://www.aafp.org/afp/20040201/548.html</ref> B grade recommendation[6]
{{subst:SORT C}} C grade recommendation
CEBM {{subst:CEBM 1a|[http://www.cebm.net/index.aspx?o=1025}} level 1a
{{subst:CEBM 1b}}<ref>http://[http://www.cebm.net/index.aspx?o=1025</ref> level 1b[7]
{{subst:CEBM 1c}} level 1c
{{subst:CEBM 2a}} level 2a
{{subst:CEBM 2b}} level 2b
{{subst:CEBM 2c}} level 2c
{{subst:CEBM 3a}} level 3a
{{subst:CEBM 3b}} level 3b
{{subst:CEBM 4}} level 4
{{subst:CEBM 5}} level 5
GRADE Recommendations {{subst:GRADE S}} strong recommendation
{{subst:GRADE W}} weak recommendation
GRADE Quality {{subst:GRADE H}} high quality evidence
{{subst:GRADE M}} moderate quality evidence
{{subst:GRADE L}} low quality evidence
{{subst:GRADE V}} very low quality evidence


  • The absence of good evidence does not always mean bad medicine
    • Skull burr holes in historic times
  • Differential interpretation
    • It is possible for respective authoritative parties to examine identical evidence bases and come to different conclusions eg ACC/AHA 2007 downgrades evidence for enoxaparin in NSTEMI[8] compared to ESC 2007[9]
    • Inconsistency of application over time by the same body. There are several important examples such as the grading of the evidence that early antibiotic use in presentations with sepsis lead to better outcomes. The Surviving Sepsis Campaign made a major change in its grading system for the evidence base between 2004 and 2008 and this appears to be the real explanation for rather different conclusions that have had major impact on worldwide treatment of sepsis from an essentially unchanged evidence base apart from the accumulation of more similar quality information[4]
  • Bias
    • An undeclared proportion of review articles on drug therapy may be ghost written[10].

See Also

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