Article Outline
Evidence-based medicine (EBM) originated at McMaster University, Hamilton, ON, Canada, where it was defined as “the integration of current best evidence with clinical expertise and patient values” by the Evidence-Based Medicine Working Group led by Drs Gordon Guyatt and David Sackett.1 EBM represents a new paradigm for radiology practice. The old paradigm relied heavily on “expert opinion,” or so-called “eminence-based” practice. This paradigm is flawed, as expert opinion often lags far behind the evidence and is not infrequently inconsistent with evidence. In addition, an individual's experience is biased by practice mix, overemphasis on more recent events, small sample size, and lack of objectivity.2 Evidence-based practice consists of 5 steps: (1) formulate answerable questions with which to search for evidence, (2) select appropriate resources and search the literature, (3) appraise the retrieved evidence for its validity and applicability by using explicit methods, (4) integrate the information with clinical expertise and unique patient needs, and (5) evaluate one's evidence-based practice and clinical performance and practice. Step 4 emphasizes the importance of clinical expertise, and that evidence alone cannot be used to make decisions but, rather, supports the decision-making process.3 Clinical expertise refers to the clinician's cumulative experience, education, and clinical skills. Patients have personal and unique concerns, expectations, and values that influence decisions regarding patient care. Without clinical expertise, practice risks becoming tyrannized by evidence, as even excellent external evidence may be inapplicable to or inappropriate for an individual patient.4
Drs Kelly and Cronin have assembled a group of experts to write about the steps involved in EBM and how EBM can be applied to radiology practice. I thank them and all of the authors for making what could be a confusing process understandable and for showing how EBM can be used by all practicing radiologists. Before you delve into the excellent chapters that these authors have provided, I invite you to take a few minutes to test your EBM IQ by answering the following 5 questions:
1.What is the greatest impediment to physicians in integrating research data into their clinical practice?
A.Insufficient time
B.Limited search skills
C.Limited access to evidence
D.Outdated evidence
2.What level of the evidence pyramid provides the best scientific information?
A.Primary literature
B.Syntheses
C.Synopses
D.Information systems
3.What percentage of medical imaging is performed by nonradiologists?
A.4%
B.12%
C.33%
D.52%
4.Which type of efficacy relates to how well new technology detects specific disease conditions?
A.Technical
B.Diagnostic
C.Therapeutic
D.Outcomes
5.What type of bias occurs because ethical and practical considerations preclude using a consistent reference standard?
A.Selection
B.Validation
C.Lead time
D.Length time
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Answers
1.A—Insufficient time. The practice of EBM requires that information be available at the right time, in the right place, and in the right format. The usefulness of medical information is directly related to the relevance and validity of the information and indirectly related to the work of accessing and applying that information.5 In 1 study conducted in 2001, Australasian physicians identified insufficient time (74%), limited search skills (41%), and limited access to evidence (43%) as impediments to making better use of research data.6
2.D—Information systems. Haynes7 described an “evidence pyramid” that ranks literature by using scientific methods. The pyramid comprises 4 levels: primary literature, syntheses, synopses, and information systems. Evidence identified at the higher echelons of this pyramid is scientifically better than that at lower levels, and if it answers a particular question or knowledge gap, searching for evidence at the base of the pyramid becomes unnecessary.1 Information systems are at the apex of the evidence hierarchy. They consist of regularly updated electronic textbooks that aim to continually supply the best available current evidence in print or electronic formats (eg, online, handheld computers, and CD-ROMs).
3.D—52%. In a 2004 report, MedPAC (Centers for Medicare and Medicaid Services Medical Payment Advisory Commission) noted that 52% of medical imaging was performed by nonradiologists.8 Research has shown that self-referral (ie, nonradiologist physicians referring their patients to receive imaging technologies in which these physicians have a financial interest) results in greater use of imaging than when clinicians refer patients to radiologists.9 The rapid progression of imaging technology has come at a significant cost, with researchers unable to keep pace, and as a result, only a modicum of scientific evidence supports many of today's imaging applications.10
4.B—Diagnostic. Drs Fryback and Thornbury were among the pioneers of diagnostic imaging technology assessment. They proposed a hierarchy of assessment for scientific technology that serves as a framework for understanding how assessing a technology relates to its diffusion and clinical implementation.11 Technical efficacy refers to the production of an image or of information and measures signal-to-noise ratio, resolution, and absence of artifact. Diagnostic efficacy relates to the impact of a test on the likelihood of a diagnosis in a patient and measures pre- and post-test probability and diagnostic certainty. Therapeutic efficacy relates to the potential of a test to change therapy for a patient, and it measures treatment plan and operative or medical treatment frequency. Outcome efficacy relates to the effect of the use of a test on patient health and measures mortality, quality-adjusted life years, and health status.
5.B—Validation. Validation bias occurs when ethical and practical considerations preclude using the same reference standard (ie, “gold standard”) to determine the “truth” about imaging diagnoses. The reference standard for patients with positive results is based on pathologic findings and may constitute an invasive procedure. For negative cases, however, it would be unethical to pursue an invasive procedure. In such circumstances, “truth” is determined by a composite standard that combines reviewers' subjective correlation of prolonged clinical follow-up, subsequent imaging studies, and intervening outcomes.10 However, the reference standard and the composite standard have different reliabilities. Because research studies cannot include all individuals in the world who have a particular clinical situation, research is conducted on samples.10 Selection bias can arise if the sample is not a true representation of the relevant underlying clinical population.12 Lead-time bias results from earlier detection of disease, which leads to longer time from diagnosis to death and an apparent survival advantage but does not truly impact the date of death.12 Length-time bias relates to the virulence of tumors. More indolent tumors are more likely to be detected by screening, whereas aggressive tumors are more likely to be detected by symptoms. This disproportionately assigns more indolent disease to the intervention group and results in the appearance of a benefit.12
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References
- Staunton M. Evidence-based radiology: Steps 1 and 2—Asking answerable questions and searching for evidence. Radiology. 2007;242:23–31
- Medina LS, Blackmore CC. Evidence-based radiology: Review and dissemination. Radiology. 2007;244:331–336
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- Sackett DL, Rosenberg WMC, Gray JAM, et al. Evidence-based medicine—What it is and what it isn't. BMJ. 1996;312:71–72http://www.cebm.net/ebm_is_isnt.asp
- Slawson DC, Shaughnessy AF, Bennett JH. Becoming a medical information master: Feeling good about not knowing everything. J Fam Pract. 1994;38:505–513
- Craig JC, Irwig LM, Stockler MR. Evidence-based tools: Useful tools for decision making. Med J Aust. 2001;174:248–253
- Haynes RB. Of studies, summaries, synopses, and systems: The “4S” evolution of services for finding best current evidence. Evid Based Ment Health. 2001;4:37–39
- Sunshine JH, Bansal S, Evens RG. Radiology performed by non-radiologists in the United States: Who does what?. Am J Roentgenol. 1993;161:419–429
- Kouri BE, Parsons RG, Alpert HR. Physician self-referral for diagnostic imaging: Review of the empiric literature. Am J Roentgenol. 2002;179:843–850
- Hillman BJ. Evidence-based radiology—A primer for referring clinicians and radiologists to improve the appropriateness of medical imaging. Medscape. http://www.medscape.com/viewprogram/4462_pnt
- Fryback DG, Thornbury JR. The efficacy of diagnostic imaging. Med Decis Mak. 1991;11:88–94
- Patz E, Goodman P, Bepler G. Screening for lung cancer. N Engl J Med. 2000;343:1627–1633
