articles Evidence-based medicine
Evidence-based medicine is a medical movement based upon the
application of the scientific method to medical practice, including
long-established existing medical traditions not yet subjected
to adequate scientific scrutiny. According to the Centre for
Evidence-Based Medicine, "Evidence-based medicine is the
conscientious, explicit and judicious use of current best evidence
in making decisions about the care of individual patients."
Using techniques from science, engineering and statistics,
such as meta-analysis of the existing literature, risk-benefit
analysis and randomized controlled trials, it aims for the ideal
that all doctors should make "conscientious, explicit,
and judicious use of current best evidence" in making decisions
about the care of individual patients.
Evidence-based medicine categorizes different types of clinical
evidence and ranks them according to the strength of their freedom
from the various biases that beset medical research. For example,
the strongest evidence for therapeutic interventions is provided
by randomized, double-blind, placebo-controlled trials involving
a homogeneous patient population and medical condition. In contrast,
patient testimonials, case reports, and even expert opinion
have little value as proof because of the placebo effect, the
biases inherent in observation and reporting of cases, difficulties
in ascertaining who is an expert, and more.
Practising evidence-based medicine implies not only clinical
expertise, but expertise in retrieving, interpreting, and applying
the results of scientific studies, and in communicating the
risks and benefit of different courses of action to patients.
For all its problems, evidence-based medicine has very successfully
demoted the ex cathedra statement of the "medical expert"
to the least valid form of evidence and all "experts"
are now expected to be able to reference their pronouncements
to the relevant literature.
Professor Archie Cochrane was a British medical researcher
whose book Effectiveness and Efficiency: Random Reflections
on Health Services (1972) and subsequent advocacy caused increasing
acceptance of the concepts behind evidence-based practice. Cochrane's
work was honoured through the naming of centres of evidence-based
medical research - Cochrane Centres - and an international organisation,
the Cochrane Collaboration. The term "evidence-based medicine"
first appeared in the medical literature in 1992 in a paper
by Guyatt et al.
Qualification of evidence
Systems to stratify evidence by quality have been developed,
such as this one by the U.S. Preventive Services Task Force:
Level I: Evidence obtained from at least one properly designed
randomized contolled trial.
Level II-1: Evidence obtained from well-designed controlled
trials without randomization.
Level II-2: Evidence obtained from well-desigend cohort or case-control
analytic studies, prferably from more than one center or research
Level II-3: Evidence obtained from multiple time series with
or without the intervention. Dramatic results in uncontrolled
could also be regarded as this type of evidence.
Level III: Opinions of respected authorities, based on clinical
experience, descriptive studies, or reports of expert committees.
The UK National Health Service uses a similar system with categories
labelled A B C D.
Categories of recommendations
In guidelines and other publications recommendations are categorised
according to the level of evidence they are based on. The U.S.
Preventive Service Task Force uses:-
Level A: Recommendations are based on good and consistent scientific
Level B: Recommendations are based on limited or inconsistent
Level C: Recommendations are based primarily on consensus and
This is a distinct and conscious improvement on older fashions
in recommendation and the interpretation of recommendations
where it was less clear which parts of a guideline were most
Limitations of available evidence
It is clearly recognised that not all evidence is made accessible,
that this can limit the effectiveness of any approach, and that
effort to reduce various publication and retrieval biases is
Failure to publish negative trials is the most obvious gap,
and moves to register all trials at the outset, and then to
pursue their results are underway. Changes in publication methods,
particularly related to the Web should reduce the difficulty
of getting a paper on a trial that concludes it did not prove
anything new, including its starting hypothesis, published.
Criticism of evidence-based medicine
Critics of evidence-based medicine state that doctors were
doing these things already, that good evidence is often deficient
in many areas, that lack of evidence and lack of benefit are
not the same, and that the more data are pooled and aggregated
the more difficult it is to compare the patients in the studies
with the patient in front of the doctor. i.e. EBM applies to
populations, not necessarily to individuals. In The limits of
evidence-based medicine, Tonelli argues that "the knowledge
gained from clinical research does not directly answer the primary
clinical question of what is best for the patient at hand."
Evidence-based medicine seems to Tonelli to discount the value
of the case study.
Evidence-based medicine is quickly rising as the 'gold standard'
for clinical practice and guidelines. The majority of current
medical and surgical practice, however, does not have a strong
literature base supporting it. There are a number of reasons.
First, in some cases, doing randomized controlled trials would
be unethical--such as in open-heart surgery. Second, certain
groups have been historically marginalized (women, racial minorities,
people with many co-morbid diseases) and thus the literature
is very sparse in areas that does not allow for generalizeability.
Third, the types of trials considered 'gold standard' (i.e.
randomized double-blind placebo-controlled trials) are very
expensive and thus funding sources play a role in what gets
investigated. For example, the government funds a large number
preventive medicine studies trying to improve public health
as a whole, pharmaceutical companies fund studies to demonstrated
efficacy and safety of particular drugs. Fourth, the studies
that make it into medical journals may not be representative
of studies that are completed or may be misleading due to conflicts
of interest (i.e. publication bias). Thus the array of evidence
available on particular therapies may not be well-represented
in the literature. Fifth, there is an enormous range of quality
of studies performed and it is difficult to generalize about
Large scale randomized control trials are extraordinarly useful
for examining discrete interventions with defined medical conditions
involved. The more complex the patient population, the conditions,
and the intervention, the more difficult it is to tease apart
effect from random variation. In this way, a number of null
studies get published, either because there is insufficient
power to show difference, or because the groups are not well-enough
Evidence-based medicine has been most practised when the intervention
tested is a drug. Applying the methods to other forms of treatment
may be harder, particularly those requiring the active participation
of the patient because blinding is is more difficult.
In managed healthcare systems evidence-based guidelines have
been used as a basis for denying insurance coverage for some
treatments some of which are held by the physicians involved
to be effective, but of which randomized controlled trials have
not yet been published.