Evidence-Based Medicine
David L. Sackett
Evidence-based medicine, whose philosophical origins extend back to mid-19th century Paris and
earlier, is the conscientious, explicit and judicious use of current best evidence in making decisions
about the care of individual patients. The practice of evidence-based medicine means integrating
individual clinical expertise with the best available external clinical evidence from systematic research.
By individual clinical expertise we mean the proficiency and judgment that we individual clinicians
acquire through clinical experience and clinical practice. Increased expertise is reflected in many
ways, but especially in more effective and efficient diagnosis and in the more thoughtful identification
and compassionate use of individual patients' predicaments, rights, and preferences in making clinical
decisions about their care. By best available external clinical evidence we mean clinically relevant
research, often from the basic sciences of medicine, but especially from patient centered clinical
research into the accuracy and precision of diagnostic tests (including the clinical examination), the
power of prognostic markers, and the efficacy and safety of therapeutic, rehabilitative, and preventive
regimens. External clinical evidence both invalidates previously accepted diagnostic tests and treatment and replaces them with new ones that are more powerful, more accurate, more efficacious,
and safer. Good doctors use both individual clinical expertise and the best available external evidence, and neither alone is enough. Without clinical expertise, practice risks becoming tyrannized
by external evidence, for even excellent external evidence may be inapplicable to or inappropriate
for an individual patient. Without current best external evidence, practice risks becoming rapidly
out of date, to the detriment of patients. The practice of evidence-based medicine is a process of
life-long, self-directed learning in which caring for our own patients creates the need for clinically
important information about diagnosis, prognosis, therapy, and other clinical and health care issues,
and in which we (1) convert these information needs into answerable questions; (2) track down,
with maximum efficiency, the best evidence with which to answer them (whether from the clinical
examination, the diagnostic laboratory from research evidence, or other sources); (3) critically appraise that evidence for its validity (closeness to the truth) and usefulness (clincial applicability); (4)
integrate this appraisal with our clinical expertise and apply it in practice; and (5) evaluate our
performance.
Copyright 9 1997 by W.B. Saunders Company
am honored to be asked to open this "festschrift" for Alvin Zipursky. In doing so, I begin by pointing out that I am neither a perinatologist nor an ephebiatrist, but a hospital-based
general physician. Accordingly, I must beg the
audience's indulgence and ask them to determine whether and how much of what I will describe among adult patients applies in perinatology.
Evidence-based medicine has been defined by
its proponents as the conscientious, explicit, and
judicious use of current best evidence in making
decisions about the care of individual patients. 1
In this definition, the practice of evidence-based
medicine means integrating individual clinical
expertise with a critical appraisal of the best available external clinical evidence from systematic
research. Individual clinical expertise means the
proficiency and j u d g m e n t that individual clinicians acquire through clinical experience and
clinical practice. Increased expertise is reflected
in many ways, but especially in more effective
and efficient diagnosis and in the more thoughtful identification and compassionate use of individual patients' predicaments, rights, and preferences in making clinical decisions about their
From the Nuffield Department of Clinical Medicine, University of
Oxford, the NHS Rg~D Centrefor Evidence-Based Medicine, Headley Way, Headington, and Oxford-Radcliffe NHS Trust, John Radcliffe Hospital, Oxford.
Supported by the Research & Development Programme of the Anglia
and Oxford Region of the National Health Service.
Address reprint requests to David L. Sackett, MD, Centrefor Evidence-Based Medicine,Johnson Radcliffe Hospital, Headington, Oxford, OX3 9DV England.
Copyright 9 1997 by W.B. Saunders Company
0146-0005/97/2101-0001 $05.00/0
Seminars in Perinatology, Vol 21, No 1 (February), 1997: pp 3-5
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David L. Sackett
care. By best available external clinical evidence
is m e a n t clinically relevant research, often from
the basic sciences of medicine, but especially
from patient-centered clinical research into the
accuracy and precision o f diagnostic tests (including the clinical examination), the power of
prognostic markers, and the efficacy and safety
o f therapeutic, rehabilitative, and preventive regimens. 2
T h e practice of evidence-based medicine is a
process of life-long, self-directed learning in
which caring for one's own patients creates the
n e e d for clinically important information about
diagnosis, prognosis, therapy, and other clinical
and health care issues, and in which its practitioners:
I. Convert these information needs into answerable questions;
2. Track down, with maximum efficiency, the
best evidence with which to answer them (and
making increasing use of secondary sources
of the best evidenceS);
3. Critically appraise that evidence for its validity
(closeness to the truth) and usefulness (clinical applicability);
4. Integrate the appraisal with clinical expertise
and apply the results in clinical practice; and
5. Evaluate one's own performance.
Evidence-based medicine is one of several disciplines that has evolved from clinical epidemiology and critical appraisal. Parallel developments,
still with the individual patient as the focus of
attention, are occurring in other clinical disciplines (eg, evidence-based surgery, evidencebased nursing, evidence-based dentistry). O t h e r
evidence-based disciplines consider the community as the focus of attention rather than
the individual patient (evidence-based public
health), or add an explicit economic element
and seek to purchase or provide that mix of
health care that will maximize some group or
public benefit (evidence-based purchasing).
Recent audits in the front lines o f clinical care
have d o c u m e n t e d that some inpatient clinical
teams in general medicine, 4 psychiatry, 5 and surgery (McCulloch P, personal communication)
have provided evidence-based care to the vast
majority of their patients. Such studies show that
busy clinicians who devote their scarce reading
time to selective, efficient, patient-driven searching, appraisal, and incorporation of the best
available evidence can practice evidence-based
medicine.
C o m m o n misconceptions about evidencebased medicine include the concern that it
might degenerate into "cook-book" medicine.
However, because it requires a bottom-up approach that integrates the best external evidence
with individual clinical expertise and patientchoice, it c a n n o t result in slavish, "cook-book"
approaches to individual patient care. External
clinical evidence can inform, but can never replace, individual clinical expertise, and it is this
expertise that decides whether the external evidence applies to the individual patient at all and,
if so, how it should be integrated into a clinical
decision. Similarly, any external guideline must
be integrated with individual clinical expertise
in deciding whether and how it matches the patient's clinical state, predicament, and preferences, and thus whether it should be applied.
Clinicians who fear top-down "cook-books" will
find the advocates of evidence-based medicine
joining them at the barricades.
Others fear that evidence-based medicine will
be hijacked by purchasers and managers to cut
the costs of health care. This would not only be
a misuse of evidence-based medicine, but suggests a fundamental misunderstanding of its financial consequences. Doctors practising evidence-based medicine will identify and apply the
most efficacious interventions to maximize the
quality and quantity of life for individual patients; this may raise rather than lower the cost
of their care.
Finally, in terms of study designs, evidencebased medicine is not restricted to randomized
trials and meta-analyses. It involves tracking
down the best external evidence with which to
answer our clinical questions. T o find out about
the accuracy of a diagnostic test, its practitioners
seek likelihood ratios, sensitivities, and specificities derived from p r o p e r cross-sectional studies
of patients clinically suspected o f harboring the
relevant disorder, not a randomized trial. For a
question about prognosis, they search for multivariate prediction rules generated from p r o p e r
follow-up studies of patients assembled at a uniform, early point in the clinical course of their
disease. Also, sometimes the evidence will come
from the basic sciences such as genetics or immunology. It is when asking questions about therapy
that the practitioners of evidence-based medi-
Evidence-Based Medicine
c i n e avoid the n o n e x p e r i m e n t a l a p p r o a c h e s , because these r o u t i n e l y lead to false-positive conclusions a b o u t efficacy. Because the r a n d o m i z e d
trial, a n d especially the systematic review of several r a n d o m i z e d trials, 6 is so m u c h m o r e likely
to i n f o r m clinicians a n d so m u c h less likely to
m i s l e a d t h e m , it has b e c o m e the " g o l d stand a r d " for j u d g i n g w h e t h e r a t r e a t m e n t does
m o r e g o o d t h a n h a r m . Clinically useful measures o f the effects o f t r e a t m e n t are sought, such
as the " n u m b e r n e e d e d to t r e a t " to p r e v e n t o n e
a d d i t i o n a l e v e n t (the r e c i p r o c a l o f the a b s o l u t e
risk r e d u c t i o n ) .
Despite its a n c i e n t origins, e v i d e n c e - b a s e d
m e d i c i n e r e m a i n s a relatively y o u n g d i s c i p l i n e
whose positive impacts 7 are j u s t b e g i n n i n g to b e
validated, a n d it will c o n t i n u e to evolve. This
e v o l u t i o n will be e n h a n c e d as several u n d e r g r a d uate, p o s t g r a d u a t e , a n d c o n t i n u i n g m e d i c a l educ a t i o n p r o g r a m s a d o p t a n d a d a p t it to t h e i r
l e a r n e r s ' needs.
F r o m the perspective o f a g e n e r a l physician,
I r e c k o n the f o r e g o i n g ideas apply equally well
to the c h a l l e n g e s o f p e r i n a t a l m e d i c i n e . However, it will be u p to the a u d i e n c e to d e c i d e
w h e t h e r this is so. For m o r e r e a d i n g , users c a n
refer to any o f the g r o w i n g n u m b e r o f texts o n
this subject 81~ o r e x a m i n e it o n the I n t e r n e t . 1~
5
References
1. Sackett DL, RosenbergWMC, GrayJAM, Richardson WS:
Evidence based medicine: What it is and what it isn't.
Br MedJ 312:71-72, 1996
2. Evidence-Based Medicine Working Group: Evidencebased medicine: A new approach to teaching the practice of medicine. JAMA 268:2420-2425, 1992
3. Examples of such secondary sources are the Cochrane
Library and journals of critically appraised clinical articles such as A CPJournal Club and Evidence-Based Medicine
4. EllisJ, Mulligan I, RoweJ, Sackett DL: Inpatient general
medicine is evidence based. Lancet 346:407-410, 1995
5. GeddesJR, Game D,Jenkins NE, et al: In-patient psychiatric care is evidence-based. Proceedings of the Royal
College of \Psychiatrists Winter Meeting. Stratford, UK,
January 23-25, 1996
6. Cook DJ, Sackett DL, Spitzer WO: Methodologic guidelines for systematic reviewsof randomized trials in health
care from the Postdam Consultation on Meta-Analysis.J
Clin Epidemiol 48:167-171, 1995
7. Bennett KJ, Sackett DL, Haynes RB, Neufeld VR: A controlled trial of teaching critical appraisal of the clinical
literature to medical students. JAMA 257:2451-2454,
1987
8. Ridsdale L: Evidence-Based General Practice. London,
WB Saunders, 1995
9. Sackett DL, Richardson SW, Rosenberg WR, Haynes RB:
Evidence-Based Medicine; How to Practice and Teach
EBM. London, Churchill-Livingstone, 1997
10. Gray JAM: Evidence-Based Health Care. London,
Churchill-Livingstone, 1997
11. Http://cebm.jr2.ox.ac.uk/ or http://hiru.mcmaster.
ca/