J Royal Society of Medicine 1995 (Nov); 88: 620–624 ~ FULL TEXT
David L Sackett FRSC MD Msc Epid FRCPC, William M C Rosenberg MA MB BS DPhil MRCP
Nuffield Department of Clinical Medicine,
Level 5, The Oxford Radcliffe NHS Trust,
Headley Way, Headington,
Oxford OX3 3DU, England
As physicians, whether serving individual patients or populations, we always have sought to base our decisions and actions on the best possible evidence. The ascendancy of the randomized trial heralded a fundamental shift in the way that we establish the clinical bases for diagnosis, prognosis, and therapeutics. The ability to track down, critically appraise (for its validity and usefulness), and incorporate this rapidly growing body of evidence into one's clinical practice has been named 'evidence-based medicine [5, 6] (EBM).
From the Full-Text Article:
In selecting a treatment, previously it had been considered
sufficient to understand the pathophysiological process in a
disorder and to prescribe drugs or other treatments that had
been shown to interrupt or otherwise modify this process.
Thus, the observation that patients with ventricular ectopic
beats following myocardial infarction were at high risk of
sudden death , coupled with the demonstration that these
extra beats could be suppressed by specific drugs, formed a
sufficient rationale for the wide-spread prescription of these
drugs to post-infarction patients with unstable cardiac
rhythms.  However, subsequent randomized controlled
trials examined outcomes, not processes, and showed that
several of these drugs increase, rather than decrease, the risk
of death in such patients, and their routine use is now
strongly discouraged.  While other randomized trials (their
total number now between 250,000 and 1,000,000!) have
confirmed the efficacy of many treatments and confirmed the
uselessness or harmfulness of many others. For example, of
226 manoeuvres that are carried out in obstetrics and
childbirth, Chalmers et al. have documented sound evidence
from randomized trials in almost a half (about 20% having
been shown to be beneficial and almost 30% found to be of
either doubtful value or harmful). 
Equally powerful methods have been developed and
applied to validate the clinical history and physical
examination, diagnostic tests, and prognostic markers.
When performed in collaboration with seasoned clinicians,
these methods often have made explicit the expert's
implicit, non-verbal diagnostic, prognostic and therapeutic
reasoning, making it possible for their trainees to replace
mere mimicry with understanding, and avoiding the
necessity for decades of experience as the only pathway to
sound clinical judgement.
Given the extremely rapid growth of randomized trials
and other rigorous clinical investigations, the issue is no
longer how little of medical practice has a firm basis in such
evidence; the issue today is how much of what is firmly
based is actually applied in the front lines of patient care. For
although we clinicians really do need to keep up to date with
clinically-important information, direct observations suggest
that we usually fail to do so. For example, a group of general
physicians responded to a questionnaire by stating that they
needed new and clinically-important information just once
or twice a week, and met these needs by consulting their
textbooks and journals.  However, the direct questioning of
these same clinicians as they saw patients identified up to 16
needs for new, clinically-important information in just half a
day, at a rate of about two questions for every three patients
they saw (about half of their questions were related to
therapeutics, and a quarter to diagnosis). As a net result, in a
typical half-day of practice, four clinical decisions would
have been altered if clinically-useful information about them
had been available and employed.
However, only 30% of these information needs were
met in the clinics and offices where the clinicians worked,
and despite their earlier claim that they predominantly used
texts and journals to gain this knowledge, direct observation
again showed that most of it was obtained by asking
colleagues. On further probing, these clinicians identified
three barriers to obtaining clinically-important information:
they lacked the time necessary for keeping up to date, their
text books were out of date, and their journals were too
disorganized to be useful. 
Unfortunately, there is growing evidence to support
clinicians' claims that our texts are out of date, even when
new. When Antman et al. compared the evidence
accumulating from randomized trials and systematic
reviews of treatments for myocardial infarction with
recommendations from contemporaneous textbooks, they
found that most texts were failing to recommend
thrombolytic therapy, even for specific indications, six
years after the first meta-analysis showed it to be
efficacious.  Moreover, these same texts and reviews were
persisting in recommending routine lignocaine prophylaxis
for ventricular fibrillation, despite ever-stronger evidence
that it was likely to be useless in lowering case-fatality.
What is the net effect of this constant but unfulfilled need
for clinically-important new information? Unfortunately, it
leads, on average, to progressive declines in our clinical
competency following the completion of our formal training.
When competency is measured by clinicians' knowledge of
even the basics of the care of disorders like hypertension, it
has been shown repeatedly that there is a statistically and
clinically significant negative correlation between our
knowledge of up to date care and the years that have
elapsed since our graduation from medical school. [9, 10]
Moreover, in one study of actual clinical behaviour, the
decision to start antihypertensive drugs was more closely
linked to the number of years since medical school
graduation in the doctor than to the severity of target
organ damage in the patient. 
Continuing Medical Education
It is clear from the foregoing that we need far readier access
to clinically-important information. No wonder, then, that
there is increasing interest in providing, and even requiring,
continuing medical education (CME), continuing professional
development, and the like. But when the same powerful
strategy for determining the efficacy of a therapeutic
regimen the randomized controlled trial has been used
to test the efficacy of CME, the results have been sobering. A
number of randomized trials have shown that traditional,
instructional CME simply fails to modify our clinical
performance and is ineffective in improving the health
outcomes of our patients. 
For example, a group of us identified 18 conditions
whose care, as documented in the clinical record, makes a
difference in patient outcomes.  We then asked a random
sample of general practitioners to rank them into a 'high-preference'
set for which they really did want to receive
CME, and a 'low preference' set for which they really did
not. Physicians with similar rankings were paired and
randomized either to a control group whose CME was
postponed for 18 months, or into an experimental group
who received CME at once for the 'high preference' set of
conditions, but had to promise to study the CME we
provided for their 'low preference' set as well. The CME
'packages' were portable, available in both written and audio
versions, had explicit objectives and several feedback tests,
and included all elements of care that were necessary for
improved patient outcomes. The clinical records of both
control and experimental physicians were examined before
and after the experimental ones received their CME,
permitting us to determine its effects on the quality of
patient care. The results were startling.
Although the knowledge of experimental physicians rose
substantially after their CME, the effects on quality of care
were both surprising and disappointing: for 'high preference'
conditions, quality of care rose about 6% (statistically
significant, but of marginal clinical significance) both among
the experimental physicians (who received CME about
them) and among control physicians (who didn't). This led
one wag on the research team to conclude: 'When you want
CME, you don't need it.' By contrast, for the 'low
preference' conditions, quality of care rose by a statistically
and clinically significant 10% among the experimental
physicians, but fell slightly among control physicians
('CME only works when you don't want it.'). Finally,
there were small declines in the quality of care provided for
conditions that had been rated as neither high nor low
preference 'CME does not cause general improvements in
the quality of care.' Thus, CME and other strategies for
Continuing Professional Development that employ just
instructional approaches do not address the problem of
our declining clinical competence.
Does anything work? Recent evidence suggests that three
broad strategies based on the principles, strategies, and
tactics of 'evidence-based medicine' (EBM) can work. By
way of background, evidence-based medicine is a short-hand
term for five linked ideas: first, that our clinical and other
health care decisions should be based on the best patient- and
population-based as well as laboratory-based evidence;
second, that the problem determines the nature and
source of evidence to be sought, rather than our habits,
protocols or traditions; third, that identifying the best
evidence calls for the integration of epidemiological and
biostatistical ways of thinking with those derived from
pathophysiology and our personal experience (examples
include using likelihood ratios to increase the power of
diagnostic information, considering inception cohorts in
making prognoses, incorporating meta-analyses of
randomized trials into decisions about therapy, and
integrating odds ratios into judgements about iatrogenic
disease); fourth, that the conclusions of this search and
critical appraisal of evidence are worthwhile only if they are
translated into actions that affect our patients; and fifth, that
we should continuously evaluate our performance in
applying these ideas.
The practice of EBM, then, is a process of life-long, selfdirected
learning in which caring for our own patients creates
the need for 61inically-important information about diagnosis,
prognosis, therapy, decision analysis, cost: utility analysis,
and other clinical and health care issues, and in which we:
convert these information needs into answerable
track down, with maximum efficiency, the best
evidence with which to answer them (whether from
the clinical examination, the diagnostic laboratory, the
published literature, or other sources)
critically appraise that evidence performance for its
validity (closeness to the truth) and usefulness (clinical
apply the results of this appraisal in our clinical practice
evaluate our performance
Recent developments and evaluations support the view
that three EBM strategies can be successful in keeping us up
to date. They consist of learning how to practice evidencebased
medicine ourselves, seeking and applying evidence-based
medical summaries produced by others, and accepting evidencebased
practice protocols, developed by our colleagues and
augmented by strategies that help us improve our clinical
Learning evidence-based medicine
The first effective strategy requires that we learn how to
become life-long, self-directed learners of evidence-based
medicine (EBM) as described above. Developed at McMaster
University in Canada, and adopted and adapted at many
other institutions around the world, this method of
mastering life-long learning skills and habits has been
evaluated in two sorts of ways. First, in a short term trial
among clinical clerks nearing graduation from medical
school, clerks who received EBM-oriented clinical tutorials
showed substantial improvements in their ability to generate
and properly defend correct diagnostic and management
decisions, while control clerks who received traditional
clinical tutorials actually made worse clinical decisions after
than before their clerkships (they had become less critical of
advice provided by authorities).  Moreover, when
McMaster graduates of their self-directed, problem-based
EBM curriculum were compared with other Canadian
medical graduates on their knowledge of clinically-important
advances in the detection, evaluation and management of
hypertension, the other Canadian graduates exhibited the
usual, progressive deterioration in this measure of clinical
competence, but the McMaster graduates remained high,
level, and up to date, even 15 years after graduation. 
Other programmes have shown that we can master EBM
skills after several years out in practice (eg. through journal
clubs or less traditional, active programmes of continuing
Seeking and applying evidence-based medical summaries generated by others
The second effective strategy applies to those of us who,
although we may not be willing or able to keep up to date by
learning evidence-based medicine ourselves, are willing to
seek out and apply specific examples of EBM produced by
others. This second approach requires that we are
predisposed to act, and that we are willing to seek
information on what to do, preferably in a compressed,
summary format that is direct and practical (this strategy is
also used by those of us who practice EBM, but is just one of
our means of keeping up to date).
In the past, this second group of clinicians were at the
mercy of the throw-away journals, drug 'detailers', and
traditional review articles, all of which have been
discredited. For example, the traditional review article, in
which an 'expert' states opinions about the proper
evaluation and management of a condition, supporting key
conclusions with selected references, has been shown to be
both non-reproducible and, as a scientific exercise, of low
mean scientific quality. For example, Oxman and Guyatt
found that experts could not agree, even among themselves,
about whether other experts who wrote review articles had:
(i) conducted a competent search for relevant studies; (ii)
generated a bias-free list of citations; (iii) appropriately
judged the scientific quality of the cited articles; or (iv)
appropriately synthesized their conclusions. Indeed, when
these experts' own review articles were subjected to these
same simple scientific principles, there was an inverse
relationship between adherence to these standards and selfprofessed
expertise (the correlation was -0.52 with an
associated P-value of 0.004) 
Rather than rely on reviews of highly variable validity,
clinicians seeking EBM have two new information sources at
their disposal. First is a new type of journal of secondary
publication that screens dozens of clinical journals for articles
that are both relevant to practice and can pass critical
appraisal quality filters, summarizes those that pass muster in
more informative' abstracts, adds commentaries from
seasoned clinicians, and introduces them with declarative
titles that give the clinical 'bottom line'. For example, the
ACP Journal Club, a publication of the American College of
Physicians, screens up to 50 journals each month for articles
on diagnosis, prognosis, therapy, aetiology, quality of care,
and health economics that are both relevant to general
physicians and adhere to rigorous methodological standards
for patient-based research (if about therapy, was there
random allocation of patients to treatments?; if about
diagnosis, was there an independent, blind comparison with
a 'gold standard ; if about prognosis, were patients
assembled at an early and uniform point in their illness?).
Each of those that pass muster (only about 13 per month!)
occupies one page of the journal, and reader surveys have
documented extraordinarily high ratings for its relevance and
usefulness. Evidence-Based Medicine, a journal with a similar
format but expanded to include surgery, obstetrics,
paediatrics, and psychiatry, will be launched by the British
Medical Journal Publications Group in 1995, jointly-edited
at McMaster University in Canada and at the Centre for
Evidence-Based Medicine at University of Oxford in the UK.
The second new information source for clinicians seeking
EBM is even more systematic. It is an outgrowth of the
scientific methods developed to combine (into overviews or
'meta-analyses') the growing numbers of randomized trials
of the same or similar treatments for the same health
condition. When properly carried out on as high a
proportion as possible of all relevant trials (since
MEDLINE misses about half the published trials  detailed
journal searching, often by hand, is required to avoid bias)
these systematic reviews provide the most accurate and
authoritative guides to therapy. The performance of
systematic reviews of therapy is so logical a step in
progress toward evidence-based health care that it has
become the focus of a rapidly growing international group of
clinicians, methodologists, and consumers who have formed
the Cochrane Collaboration  (a thousand strong by the start
of 1995, and doubling every 6 months). The systematic
reviews that are beginning to flow from this unselfish
collaboration, updated each time an important new trial is
reported, are providing the highest levels of evidence ever
achieved on the efficacy of preventive, therapeutic, and
rehabilitative regimens. They will be published on computer
diskette and compact disk, on the Internet, and in a variety
of other forms (including the EBM journals of secondary
Thus, busy clinicians seeking clinical 'bottom lines' will
increasingly be able to eschew non-expert 'expert' reviews
and self-serving commercial sources and find brief but valid
summaries of best evidence on a growing array of clinical
topics, appraised according to uniform, established
principles. Moreover, when 'clinical guidelines' and other
practice recommendations are based on this level of evidence
(most to date are not), they become worth following.
Accepting evidence-based practice protocols developed by colleagues
Third, even when we, for whatever reason, fail both to learn
medicine if we acknowledge the problems of becoming out
of date, accept evidence-based practice protocols developed
by our colleagues, and submit ourselves to some
combination of the four strategies that have been proven
(in randomized trials, of course!) to alter our clinical
practice for the better : first, receiving individualized audit
and feedback about what we are doing right and wrong (the
growing use of computers in clinical practice enhances the
potential effectiveness of this strategy ); second, receiving
advice from a respected teacher (who has learned EBM);
third, being visited by a non-commercial 'detailer' (who is
informing and encouraging us about specific evidence-based
ways of caring for patients rather than exhorting us to
prescribe specific drugs); and fourth, taking a 'minisabbatical'
or preceptorship in a place where EBM is
These strategies have been shown to be effective in
helping us overcome at least some of the barriers imposed by
both the lack of clinically important information and the
social and professional context within which we practice
medicine, and can help us move ourselves from opinionbased
practice toward evidence-based medicine.
It is not news that medicine and all other health care are
rapidly changing. ('The future is already here; it just isn't
evenly distributed yet.') Consequently, the advocacy of yet
another change, the adoption of EBM, risks making
impossible demands on an already over-burdened
profession and health care system. However, many of the
other changes we face become easier to enact, not more
difficult, through the adoption of EBM:
with reductions in junior doctors' hours comes the need
for greater efficiency, both on their part and on the part
of the consultants they leave behind; EBM can help here
by identifying which time- and resource-intensive
manoeuvres should be dropped and which retained
similarly, EBM helps us identify those clinical acts whose
performance will meet the growing demands for
increased quality, and will help with their appropriate
purchasing and provision
as more clinical care is provided by health care teams,
EBM provides a common language through which we
can communicate and rules of evidence by which we can
agree on who will do what and to whom
EBM employs identical strategies and tactics for clinical
learning for both undergraduate and postgraduate
education, including continuing education and
professional development. Not only does this make
for far easier (reinforced, 'spiral') learning; it also makes
for far easier teaching and resource-development
(funding and 'training the trainers'), since EBM
approaches meet the recommendations now appearing
and to seek out EBM, we still can practise up to date from commissioning bodies and standing committees
addressing the education of both future  and current  clinicians.
Finally, evidence-based medicine provides us with not
only the opportunity to remain up-to-date in our own
and related clinical fields, but also with the scientific
framework within which to identify and answer priority
questons about the effectiveness of the entire range of
clinical and other health care
Warm thanks to lain Chalmers, Muir
Gray, Lelia Duley, Tony Hope, Nicholas Hicks, Martin
Dawes, Ruairidh Milne, and Douglas Altman for their
critiques of earlier versions of this essay.
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