Evidence-based medicine

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'Wedge' of Best Evidence - Start at the top
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Last Update

  • Updated.jpg 1 November 2016


See also Evidence-based health care | Evidence-based medicine - history | Evidence-based practice workshops | Médecine fondée sur les faits

Evidence-based medicine (also evidence-based health care) is the practice of integrating clinical experience and patient values with the best available evidence to provide patient care and to optimize the outcomes of that care. Health providers who make clinical decisions using EBM principles can be compared to financial analysts with business models. A balance sheet of benefits and harms is created based on a combination of research findings and the profiles of patients; clinicians subsequently make informed decisions in the best interests of patients.

Steps towards EBM

Incorporating the best available research information is key to EBM decision-making and involves four essential steps:

  1. Asking answerable questions
  2. Accessing the best information
  3. Appraising the information obtained for validity and relevance
  4. Applying the information to specific patient care

It's critical to frame clinical questions appropriately. An average of 1-2 questions arises in each patient consultation and can go up to 5 for each patient. One third of questions relate to treatments while a quarter relate to diagnosis. Background questions that address basic physiological processes are found in textbooks while foreground questions that relate to clinical decision-making are found in EBM tools. Framing good clinical questions start by defining a population and health problem, an intervention or exposure and a suitable comparison for the intervention. An example of a patient’s clinical question that relates to EBM may be rephrased as "In asymptomatic adult women at risk of breast cancer (population), does screening (intervention) reduce likelihood of breast cancer fatality (outcome) compared with routine self-examination (comparator)?"

Seminal text(s)

Assessing the evidence

In accessing the best evidence, summarized primary studies and findings such as evidence-based guidelines and systematic reviews should be examined. EBM information sources should be of high quality, clinically applicable, comprehensive and user-friendly. Should important summarized information be unavailable, the next best option is to access the primary research itself. The most common filter of primary research can be located in PubMed free online.

EBM is modeled on levels of evidence that correspond to how primary research is conducted. The “prospective, double-blind, randomized, controlled” study is the gold standard on which clinical evidence is created. A prospective study involves following the study group over a period of time. Double blinding involves the subject and the researcher not being aware of the identity of the intervention. Randomization involves reducing bias in the choice of subjects for the study. The control is often placebo but can be currently available treatments -- thereby adding further weight to the intervention outcomes. At the lower levels of evidence, studies consist of case reports and other anecdotal comments.

Once evidence is gathered, it should be appraised for quality and relevance. Poor quality studies are known to overestimate the benefits of interventions by 30%+ and this can make ineffective interventions appear to be effective. The clinician practicing EBM at this stage has to query how strong the evidence is, how big the effect is and whether the effect matters to patients. The statistical precision of results is often important as it points to whether the study’s findings can be explained by chance. The last stage is for clinicians to decide whether the best available research relates to an individual patient and if so, how the evidence can determine a course of action in diagnosing or treating the patient.

In adopting EBM, clinicians cite limited time, search skills and access to evidence as impeding their use of information. In most clinical situations, EBM is a core foundation on which sound decisions are made. The final decision is made using clinical experience, the patient’s values and costs of therapy. Clinical experience is critical especially where it is a highly urgent situation, or if lack of information or a patient's unique problems are beyond the direct applicability of evidence.

New EBM tools and supports are being made available to assist clinicians. These include newer and more sophisticated computer software and clinical support tools, mobile devices that clinicians can carry with them at points of patient care. Several initiatives encourage EBM such as the Cochrane Collaboration, which develops systematic reviews. Others include Bandolier, McMaster University, the Centre for Evidence-based Medicine, the Evidence-Based Medicine Resource Centre as well as other government and non-profit organizations.


Evidence-based movement of the 20th century

The evaluation of interventions has existed for centuries but Scottish epidemiologist, Archie Cochrane, promulgated the principles in his 1972 book Effectiveness and efficiency: random reflections on health services. His advocacy of empirical methods has placed an emphasis on using the evidence from research trials in order to make clinical decisions. Cochrane's work is honoured through the international Cochrane Collaboration and the Cochrane Library. Explicit methodologies are used in the Cochrane initiatives to determine "best evidence" and were established by prominent names at McMaster such as David Sackett and Gordon Guyatt.

The term "evidence-based medicine" can be traced back to a 1992 paper by Gordon Guyatt and others. During the 1990s, evidence-based medicine emerged as one of the premier research methods in evaluating clinical interventions. What made evidence-based health care different was that it combined the best medical evidence with the values of patients. The available medical literature that applied to patients made it possible to diagnose their problems and to choose treatments that were quantitatively evaluated. By using these methods in large groups of patients with the same illness, doctors were able to develop clinical practice guidelines for the evaluation and treatment of human diseases and conditions. Clinical practice guidelines have been used to aid physicians in the evaluation of their performance and identifying new areas for study.

Systematic reviews of the medical literature, large randomized controlled trials (the best way to assess efficacy of treatments), and large prospective studies (followed up over time) are three potentially important types of medical research as they are seen to be high up on the evidence-based pyramid of evidence about tests and treatments. Reports of the experiences of individual patients or small groups provide less reliable evidence, although they too can provide insight into the many possible adverse effects of treatments.


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