Evidence-based medicine

Evidence-based medicine (EBM) is a medical movement based upon the application of the scientific method to medical practice, recognizing that many long-established medical traditions are 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."

Overview
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 and other healthcare professionals should make "conscientious, explicit, and judicious use of current best evidence" in their everyday practice.

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. One way that physicians facilitate the integration of evidence-based medicine in daily practice is via participation in a journal club.

History
Professor Archie Cochrane was a Scottish epidemiologist 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 &mdash; Cochrane Centres &mdash; 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.

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 controlled trial.
 * Level II-1: Evidence obtained from well-designed controlled trials without randomization.
 * Level II-2: Evidence obtained from well-designed cohort or case-control analytic studies, preferably 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 trials might 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, and D.

Categories of recommendations
In guidelines and other publications, recommendations are classified according to the level of evidence on which they are based. 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.

Oxford Centre for Evidence-based Medicine uses these "grades of recommendations" according to the study designs and critical appraisal of prevention, diagnosis, prognosis, therapy, and harm studies:


 * Level A: consistent Randomised Controlled Clinical Trial, Cohort Study, All or None, Clinical Decision Rule validated in different populations.


 * Level B: consistent Retrospective Cohort, Exploratory Cohort, Ecological Study, Outcomes Research, Case-Control Study; or extrapolations from level A studies.


 * Level C: Case-series Study or extrapolations from level B studies


 * Level D: Expert opinion without explicit critical appraisal, or based on physiology, bench research or first principles

"Extrapolations" are where data is used in a situation which has potentially clinically important differences than the original study situation. Other explanations described elsewhere in the Centre’s pages

Limitations of available evidence
It is 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 maintain 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." Tonelli suggests that proponents of evidence-based medicine discount the value of clinical experience.

Although evidence-based medicine is quickly becoming the "gold standard" for clinical practice and treatment guidelines, there are a number of reasons why most current medical and surgical practices do not have a strong literature base supporting them. First, in some cases, conducting randomized controlled trials would be unethical--such as in open-heart surgery--although observational studies are designed to address these problems to some degree. Second, certain groups have been historically under-researched (women, racial minorities, people with many co-morbid diseases) and thus the literature is very sparse in areas that do 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 of preventive medicine studies that endeavor to improve public health as a whole, while pharmaceutical companies fund studies intended to demonstrate the efficacy and safety of particular drugs. Fourth, the studies that are published in medical journals may not be representative of all the studies that are completed on a given topic (published and unpublished) or may be misleading due to conflicts of interest (i.e. publication bias). Thus the array of evidence available on particular therapies may not be well-represented in the literature. Fifth, there is an enormous range in the quality of studies performed, making it difficult to generalize about the results.

Large randomized controlled trials are extraordinarly useful for examining discrete interventions for carefully defined medical conditions. The more complex the patient population, the conditions, and the intervention, the more difficult it is to separate the treatment effect from random variation. Because of this, a number of studies obtain insignificant results, either because there is insufficient power to show a 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 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.

Note

 * Guyatt G, Cairns J, Churchill D, et al. [&#8216;Evidence-Based Medicine Working Group&#8217;] Evidence-based medicine. A new approach to teaching the practice of medicine. JAMA 1992;268:2420-5. PMID 1404801.