Evidence-based medicine

Evidence-based medicine (EBM) applies the scientific method to medical practice. 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.".

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, recommendation for a clinical service is classified by the balance of risk versus benefit of the service and the level of evidence on which this information is based. The U.S. Preventive Service Task Force uses:
*Level A: Good scientific evidence suggests that the benefits of the clinical service substantially outweighs the potential risks. Clinicians should discuss the service with eligible patients.
*Level B: At least fair scientific evidence suggests that the benefits of the clinical service outweights the potential risks. Clinicians should discuss the service with eligible patients.
*Level C: At least fair scientific evidence suggests that there are benefits provided by the clinical service, but the balance between benefits and risks are too close for making general recommendations. Clinicians need not offer it unless there are individual considerations.
*Level D: At least fair scientific evidence suggests that the risks of the clinical service outweighs potential benefits. Clinicans should not routinely offer the service to asymptomatic patients.
*Level I: Scientific evidence is lacking, of poor quality, or conflicting, such that the risk versus benefit balance cannot be assessed. Clinicians should help patients understand the uncertainty surrounding the clinical service.

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.

The Oxford Centre for Evidence-based Medicine uses these levels of evidence (LOE) and "grades of recommendations" according to the study designs and critical appraisal of prevention, diagnosis, prognosis, therapy, and harm studies: Oxford Centre for Evidence-based Medicine Levels of Evidence and Grades of Recommendation
*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.

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 obtaining publication for a paper on a trial that concludes it did not prove anything new, including its starting hypothesis.

Treatment effectiveness reported from clinical studies may be higher than that achieved in later routine clinical practice due to the closer patient monitoring during trials that leads to much higher compliance rates. "Patient Compliance with statins" ''Bandolier Review 2004

Criticism of evidence-based medicine

Critics of EBM say 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 â€" that is, EBM applies to populations, not necessarily to individuals. In The limits of evidence-based medicine{{cite web