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Evidence-based medicine

Evidence-based medicine is a medical movement based upon the application of the scientific method to medical practice, including long-established existing medical traditions not yet subjected to adequate scientific scrutiny. According to the Centre for Evidence-Based Medicine, "Evidence-based medicine is the conscientious, explicit and judicious use of current best evidence in making decisions about the care of individual patients."



Using techniques from science, engineering and statistics, such as meta-analysis of the existing literature, risk-benefit analysis and randomized controlled trials, it aims for the ideal that all doctors should make "conscientious, explicit, and judicious use of current best evidence" in making decisions about the care of individual patients.

Evidence-based medicine categorizes different types of clinical evidence and ranks them according to usefulness for guiding a treatment decision for an individual patient. For example, the strongest evidence is provided by randomized controlled prospective trials involving similar patients with similar conditions. In contrast, testimonials, hearsay and mystical arguments have little value as proof because the placebo effect, random events and observer bias distort perceptions.

Practising evidence-based medicine implies not only clinical expertise, but expertise in retrieving, interpreting, and applying the results of scientific studies, and in communicating the risks and benefit of different courses of action to patients.

For all its problems, evidence-based medicine has very successfully demoted the ex cathedra statement of the "medical expert" to the least valid form of evidence and all "experts" are now expected to be able to reference their pronouncements to the relevant literature.


Professor Archie Cochrane was a British medical researcher whose book Effectiveness and Efficiency: Random Reflections on Health Services (1972) and subsequent advocacy caused increasing acceptance of the evidence-based medicine concept. Cochrane's work was honoured through the naming of centres of evidence-based medical research — Cochrane Centres — and an international organisation, the Cochrane Collaboration.

Qualification of evidence

The U.S. Preventive Services Task Force developped the following system to asses quality of medical evidence:

  • Level I: Evidence obtained from at least one properly designed randomized contolled trial.
  • Level II-1: Evidence obtained from well-designed controlled trials without randomization.
  • Level II-2: Evidence obtained from well-desigend cohort or case-control analytic studies, prferably from more than one center or research group.
  • Level II-3: Evidence obtained from multiple time series with or without the intervention. Dramatic results in uncontrolled could also be regarded as this type of evidence.
  • Level III: Opinions of restected authorities, based on clinical experience, descriptive studies, or reports of expert committees.

Categories of evidence

The U.S. Preventive Service Task Force categorizes medical evidence as follows:

  • Level A: Recommendations are based on good and consistent scientific evidence.
  • Level B: Recommendations are based on limited or inconsistent scientific evidence.
  • Level C: Recommendations are based primarily on consensus and expert opinion.

Criticism of evidence-based medicine

Critics of evidence-based medicine state that doctors were doing these things already, that good evidence is often deficient in many areas, that lack of evidence and lack of benefit are not the same, and that the more data are pooled and aggregated the more difficult it is to compare the patients in the studies with the patient in front of the doctor. i.e. EBM applies to populations, not necessarily to individuals. In The limits of evidence-based medicine, Tonelli argues that "the knowledge gained from clinical research does not directly answer the primary clinical question of what is best for the patient at hand." Evidence-based medicine seems to them to discount the value of the case study.

Evidence-based medicine is quickly rising as the 'gold standard' for clinical practice and guidelines. The majority of current medical and surgical practice, however, does not have a strong literature base supporting it. There are a number of reasons. First, in some cases, doing randomized controlled trials would be unethical--such as in open-heart surgery. Second, certain groups have been historically marginalized (women, racial minorities, people with many co-morbid diseases) and thus the literature is very sparse in areas that does not allow for generalizeability. Third, the types of trials considered 'gold standard' (i.e. randomized double-blind placebo-controlled trials) are very expensive and thus funding sources play a role in what gets investigated. For example, the government funds a large number preventive medicine studies trying to improve public health as a whole, pharmaceutical companies fund studies to demonstrated efficacy and safety of particular drugs. Fourth, the studies that make it into medical journals may not be representative of studies that are completed or may be misleading due to conflicts of interest (i.e. publication bias).[1] Thus the array of evidence available on particular therapies may not be well-represented in the literature. Fifth, there is an enormous range of quality of studies performed and it is difficult to generalize about results.

Large scale randomized control trials are extraordinarly useful for examining discrete interventions with defined medical conditions involved. The more complex the patient population, the conditions, and the intervention, the more difficult it is to tease apart effect from random variation. In this way, a number of null studies get published, either because there is insufficient power to show difference, or because the groups are not well-enough 'controlled.'

The primary problem is that evidence-based medicine is most effective when testing the effectiveness of drugs and may not be appropriate for other forms of treatment, particularly those requiring the active participation of the patient.

In America, evidence-based guidelines are used as the basis for denying insurance coverage for treatments which are generally held by physicians to be effective, but for which randomized, controlled trials have not yet been held.

See also

External links

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