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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 the strength of their freedom from the various biases that beset medical research. For example, the strongest evidence for therapeutic interventions is provided by randomized, double-blind, placebo-controlled trials involving a homogeneous patient population and medical condition. In contrast, patient testimonials, case reports, and even expert opinion have little value as proof because of the placebo effect, the biases inherent in observation and reporting of cases, difficulties in ascertaining who is an expert, and more.

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 concepts behind evidence-based practice. Cochrane's work was honoured through the naming of centres of evidence-based medical research - Cochrane Centres - and an international organisation, the Cochrane Collaboration. The term "evidence-based medicine" first appeared in the medical literature in 1992 in a paper by Guyatt et al[1].

    Qualification of evidence

Systems to stratify evidence by quality have been developed, such as this one by the U.S. Preventive Services Task Force:

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 respected authorities, based on clinical experience, descriptive studies, or reports of expert committees.
The UK National Health Service uses a similar system with categories labelled A B C D.

    Categories of recommendations

In guidelines and other publications recommendations are categorised according to the level of evidence they are based on. The U.S. Preventive Service Task Force uses:-

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.
This is a distinct and conscious improvement on older fashions in recommendation and the interpretation of recommendations where it was less clear which parts of a guideline were most firmly established.

   Limitations of available evidence

It is clearly recognised that not all evidence is made accessible, that this can limit the effectiveness of any approach, and that effort to reduce various publication and retrieval biases is required.

Failure to publish negative trials is the most obvious gap, and moves to register all trials at the outset, and then to pursue their results are underway. Changes in publication methods, particularly related to the Web should reduce the difficulty of getting a paper on a trial that concludes it did not prove anything new, including its starting hypothesis, published.

   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 Tonelli 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).[2] 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.'

Evidence-based medicine has been most practised when the intervention tested is a drug. Applying the methods to other forms of treatment may be harder, particularly those requiring the active participation of the patient because blinding is is more difficult.

In managed healthcare systems evidence-based guidelines have been used as a basis for denying insurance coverage for some treatments some of which are held by the physicians involved to be effective, but of which randomized controlled trials have not yet been published.

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