Health Questions and Answers

EVIDENCE-BASED MEDICINE

What is evidence-based medicine (EBM)?
EBM is an approach to medicine that integrates the current best evidence, clinical expertise, and patient values to optimize clinical outcomes and quality of life. With EBM comes the recognition that intuition, unsystematic clinical experience, and speculative pathophysiologic rationale are insufficient grounds for clinical decision-making. Instead, EBM maintains that a hierarchy of best research evidence exists. It is this best research evidence, based on clinically relevant research, that is to serve as the foundation for clinical decision making.

When and how did EBM first develop?
The roots of EBM date to the late 1970s, when a group of clinical epidemiologists, led by David Sackett and his colleagues at McMaster University, began preparing a series of articles advising clinicians how to read clinical journals and apply evidence from the literature to direct patient care.

Who first used the term evidence-based medicine?
The term was first used by Gordon Guyatt, MD, in 1990 while serving as residency director of the internal medicine program at McMaster.

What constitutes the evidence in EBM?
In EBM, any empirical observation about the relationship between event and clinical outcome constitutes potential evidence. Nonetheless, all evidence should not be viewed as equal in making clinical decisions.

What is the hierarchy of evidence used in EBM?
The strength of evidence provided by the unsystematic observations of an individual clinician should not be viewed the same as the evidence provided by systematic and controlled clinical trials. An example of a hierarchy of strength of evidence for treatment decisions is listed, from most preferable to least, as follows:

  • N of 1 randomized controlled trials
  • A systematic review of randomized controlled trials
  • A single randomized trial
  • A systematic review of observation studies
  • A single observational study
  • Physiologic studies
  • An unsystematic clinical observation

Guyatt GH, Haynes B, Jaeschke R, et al: Introduction: The philosophy of evidence-based medicine. In Guyatt GH, Rennie D (eds): Users’ Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice. Chicago, American Medical Association, 2002, pp 5-20.

How does the hierarchy of evidence rank randomized controlled studies versus observational studies? How does it rank multiple studies versus single studies?
The hierarchy demonstrates that, in general, the strength of evidence increases with randomized controlled studies, compared with observational studies. The hierarchy also demonstrates that the strength of evidence increases with multiple studies, compared to individual studies.

What must clinicians remember when generalizing results from studies to individual patients?
When considering available research evidence in making decisions about the treatment of their patients, clinicians most often generalize results from studies of other people, which can weaken causal inferences about treatment effectiveness; clinicians must remember that there are still important questions to be answered about the applicability of research findings from the study group to the treatment of an individual patient outside the study.

How is the N of 1 randomized controlled trial conducted?
An individual patient undergoes pairs of treatment periods: the patient receives an experimental treatment in one period of each of the paired treatment periods and a placebo or alternative treatment in the other period. If feasible, the clinician and patient are blinded to the allocation of treatment and the order of treatment is randomized. Typically, clinicians and patients make quantitative ratings of outcomes, and treatment periods are then alternated until the clinician and the patient are convinced that the patient is, or is not, receiving benefit from the experimental treatment.

What are the strengths and weaknesses of N of 1 randomized controlled clinical trials?
The strengths are that they provide definitive evidence of effectiveness in individual patients, they are feasible, and they can lead to long-term changes in treatment administration and effects.
Weaknesses include the fact that such trials require a high degree of interest, time, and cooperation between clinician and patient. N of 1 trials are not usually appropriate for short-term problems, therapeutic cures, determining long-term outcomes, or disorders that are rare.
Guyatt GH, Keller JL, Jaeschke R, et al. The n-of-1 randomized control trial: Clinical usefulness. Our three-year experience. Ann Intern Med 112:293-299, 1990.
Mahon J, Laupacis A, Donner A, Wood T: Randomised study of n of 1 trials versus standard practice. BMJ 312:1069-1074, 1996.

What is the difference between background and foreground questions in EBM?
One of most difficult aspects of applying EBM to clinical practice is formulating answerable clinical questions for which there are best current evidence available. EBM considers clinical questions in two broad categories: background and foreground questions. Background questions ask for general knowledge about a disorder and attempt to answer the who, what, when, where, why, and how of the disorder or an aspect of the disorder. Foreground questions ask for specific information about managing patients with a disorder and typically ask about the patient, the problem, interventions, and clinical outcomes. Generally, as experience with a disorder increases, the clinician moves from asking a preponderance of background questions to foreground questions.

What are the best sources for finding current best evidence?
Electronic evidence databases, evidence-based journals, and online services are sources that provide significant current best evidence. These sources sharply contrast traditional medical textbooks, which are often not the most appropriate method of finding current best evidence. Although most medical textbooks often provide useful information on pathophysiology, they typically become quickly out-of-date with regard to information on cause, diagnosis, prognosis, prevention, and treatment of a given disorder.

List some online resources that are particularly useful for evidence-based medicine.
ONLINE RESOURCES PARTICULARLY USEFUL FOR EVIDENCE-BASED MEDICINE
ACP Journal Club http://www.acpjc.org
ACP Medicine http://www.acpmedicine.com
Best Bets http://www.bestbets.org/
Centre for Evidence-Based Medicine http://www.cebm.net/index.asp
Clinical Evidence http://www.clinicalevidence.org/
Clinical practice guidelines http://www.guidelines.gov
Cochrane Library http://www3.interscience.wiley.com/cgi-bin/mrwhome/106568753/HOME
emedicine http://www.emedicine.com
Evidence-Based Medicine Reviews (OVID) http://www.ovid.com
Evidence-Based http://cebm.jr2.ox.ac.uk
Harrisons Online http://www.harrisonsonline.com
London Links journal listings http://www.londonlinks.ac.uk
MD Consult http://www.mdconsult.com
Medical Matrix http://www.medmatrix.org
Medline/PubMed http://www.pubmed.gov
Medscape http://www.medscape.com
ScHarr Netting the Evidence http://www.shef.ac.uk/~scharr/ir/netting
United Health Foundation http://www.unitedhealthfoundation.org
UpToDate http://www.uptodate.com
WebMD http://www.webmd.com

Last updated: March 15, 2010
Reference:
1. Dalla Vecchia LK, Grosfeld JL, West KW, et al: Intestinal atresia and stenosis: A 25-year experience with 277 cases. Arch Surg 133:490-496, 1998.
2. Guyatt GH, Haynes B, Jaeschke R, et al: Introduction: The philosophy of evidence-based medicine. In Guyatt GH, Rennie D (eds): Users’ Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice. Chicago, American Medical Association, 2002, pp 5-20.
3. Guyatt GH, Keller JL, Jaeschke R, et al: The n-of-1 randomized control trial: Clinical usefulness. Our three-year experience. Ann Intern Med 112:293-299, 1990.
4. Guyatt G, Rennie D: Users’ Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice. Chicago, American Medical Association, 2002.
5. Larson EB, Ellsworth AJ, Oas J: Randomized clinical trials in single patients during a 2-year period. JAMA 270:2708-2712, 1993.
6. Levine M, Haslam D, Walter S, et al: Harm. In Guyatt GH, Rennie D (eds): Users’ Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice. Chicago, American Medical Association, 2002, pp 121-153.
7. Mahon J, Laupacis A, Donner A, Wood T: Randomised study of n of 1 trials versus standard practice. BMJ 312:1069-1074, 1996.
8. Millar AJ, Cywes S: Caustic strictures of the esophagus. In O’Neill JA, Rowe MI, Grosfeld JL, Coran AG (eds): Pediatric Surgery, 5th ed. St. Louis, Mosby, 1998, pp 969-979.
9. Sackett DL, Straus S, Richardson S, et al: Evidence-based Medicine: How to Practice and Teach EBM, 2nd ed. London, Churchill Livingstone, 2000.

2 Responses to “EVIDENCE-BASED MEDICINE”

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