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Does evidence based medicine adversely affect clinical judgment?

BMJ 2018; 362 doi: (Published 16 July 2018) Cite this as: BMJ 2018;362:k2799
  1. Michel Accad, cardiologist1,
  2. Darrel Francis, professor of cardiology2
  1. 1San Francisco, USA
  2. 2National Heart and Lung Institute, Imperial College, London
  1. Correspondence to: M Accad mfa{at}, D Francis d.francis{at}

For practical and theoretical reasons, says Michel Accad, evidence based medicine is flawed and leads to standardised rather than excellent individualised care, but Darrel Francis argues that it protects patients from seemingly rational actions that cause more harm than good

Yes—Michel Accad

Consider Dr Smith, a conscientious physician who keeps abreast of the medical literature and is attentive to the individual needs of her patients. Smith is well respected by her colleagues for the wisdom of her decisions.

For example, when she sees a patient with chest pain that is unlikely to be ischaemic, Smith rarely orders a stress test. She knows that the risk of a false positive result outweighs the possibility of diagnosing coronary disease.

Sometimes, however, Smith may deviate from that practice. She believes that, under certain circumstances, after considering all alternative courses of action, it may turn out to be in a patient’s best interest to disregard the objective evidence on stress tests. Can Smith be said to practise evidence based medicine (EBM)?

At first glance, proponents of EBM seem willing to answer in the affirmative and grant Smith her decisional prerogative. For example, a well established definition of the EBM is “the conscientious, explicit, and judicious use of best evidence in making decisions about the care of individual patients.”1

Judicious use of best evidence implies that evidence is subject to judgment. Depending on the circumstances, a physician can choose to apply or ignore the evidence even if the evidence is “best.” Judgment rules. Case closed.

But this lenient interpretation runs the risk of trivialising EBM. After all, what’s the point of calling attention to the importance of the evidence if that evidence can be discarded willy-nilly by the clinical judgment of the doctor? Isn’t EBM meant as a safeguard against the reasoning errors of physicians?

To defend the importance of EBM, its architects feel compelled to backpedal. They specify that “good doctors use both individual clinical expertise and the best available external evidence, and neither alone is enough.”1 Evidence, then, is a check against clinical judgment gone awry.

Something’s amiss

Unfortunately, the proposition doesn’t hold up. How can evidence be a check on judgment when judgment is obviously required to appraise the quality of the evidence and its relevance to the patient at hand? Something’s amiss.

What’s amiss is that EBM’s professed respect for clinical judgment is, at best, only wishful or, at worst, simply disingenuous.

A clue to that effect is provided by US EBM guru David Eddy, originator of the term “evidence based,” who recently remarked that the evidence based movement arose primarily from a desire to standardise care, not to individualise it.2

Eddy’s point is obvious when we consider the institutions and organisations that have enthusiastically embraced EBM from the start: national health systems, private healthcare payers, regulators, drug companies, public health departments, and disease specific interest groups have all taken a keen interest in EBM precisely for its ability to formulate standards of care—that is, clinical guidelines—and to encourage, reward,3 or even oblige45 doctors to practise in accordance with those standards.

But practising according to standards is antithetical to practising according to clinical judgment: standardisation can only identify best practices for an “average patient” under average conditions. Clinical judgment is personal and seeks to decide what is best for this specific patient at this specific time. Standardisation aims to improve outcomes; clinical judgment aims to improve health. The two goals are clearly distinct.

EBM’s bias

EBM may allege to reduce cognitive bias, but it introduces a bias of its own: the tendency to treat according to population norms rather than personal needs,6 a “groupthink” of sorts.7 Standardisation informed by EBM, then, will necessarily deny Dr Smith the freedom to care for her patient on the basis of her judgment. It is no longer judgment that rules but evidence that decides.

EBM’s adverse influence on clinical judgment is not unexpected. Early critics of EBM pointed out its internal contradictions: individual decision making cannot be based on general evidence, and clinical judgment cannot be specified by methodological formalities.8910

EBM may allege to have been hijacked11 or corrupted,12 but it contains within itself the seeds of its own demise. The confused premises on which it is based can only confuse the clinical judgment that it claims to assist.13

No— Darrel Francis

Imagine an electrician comes to your house to repair a washing machine that repeatedly breaks down. She adjusts a screw deep inside the machine.

How would you feel to learn that this adjustment had never been found to reduce recurrence of breakdowns? And that it had multiple consequences whose net effect was unknown?

Evidence based medicine expects doctors to choose among tweaks that have been found to do more good than harm; not just among tweaks that they or their institution like to do for financial reasons or to feel good about themselves.

Draw of autonomy

The greatest pleasure in life is freedom to do what one wants. Inevitably we doctors dislike the straitjacket of EBM restricting our freedom to treat patients with water (because we like the sound of homeopathy) or diagnose their diseases by feeling the bumps on their head (because we read about it in a magazine). It is annoying to be limited to things that somewhere, somehow, someday, genuinely worked.

Can’t we be trusted to spot a nonsensical therapy or diagnostic test? No. Humans are easily fooled, and doctors are—for now—human. The real danger is not obviously nonsensical ideas but seemingly logical ones. Only recently, our profession believed that physical and mental disorders arose from imbalance of the four humours—blood, yellow bile, black bile, and phlegm. A patient who had disordered blood would obviously improve with bloodletting. Years of experience of patients recovering after thoughtful, personalised bloodletting were confirmation of efficacy.

Today’s experts in homeopathy and astrology quite rightly give level C (proof by expert consensus) or level B (proof by non-randomised observations) recommendations for their specialised techniques (using the terminology used in cardiology14).

We are all trapped in our bubble of beliefs

Neither the medieval believers in humours nor the modern homeopaths and astrologers are amenable to the suggestion that their mechanistic world view is nonsensical. However, this should not make us smirk with smug superiority but heighten our awareness that we, too, are trapped within our bubble of beliefs. Consensus of beliefs does not automatically make them correct.

EBM protects our patients not from nonsensical therapies but from rational ones that cause more harm than good. The human body is incomprehensibly complex. Unlike complex computer software, in which each component has precisely specified behaviours designed to fit together in a manner comprehensible by human software engineers, human biology underwent natural selection for providing a competitive edge, rather than for ease of describing. Moreover, even the language we use in medicine is almost incapable of describing dependence on more than one variable, never mind thousands. For example, how does a doctor describe non-mathematically the dependence of z on x and y in the relation z=(x+10)(y+10)2?

We consistently overestimate our ability to understand biology well enough to personalise tests and treatments beneficially. Personalisation may be harmless fun and even increase the placebo effect, but we should be under no illusion that we have done anything useful.

Some people criticise EBM for failing to curtail the overuse of therapies in fee-for-service systems such as in the US. However, EBM is only a framework for thinking and cannot stop doctors responding to incentives. (The clue is in their name, after all.)

My favourite example of the need for EBM, even for astute clinical scientists, was inadvertently provided by a friend, a veteran of many guideline writing committees, who said:

“We are not treating many HF [heart failure] patients who would benefit from CRT [cardiac resynchronisation therapy] simply because there are no scientifically evidence-based guidelines telling us to. I have used CRT successfully in patients with narrow QRS [complex], and so have many others. The medical literature supporting this belief is increasing with observational studies and anecdotal cases of success in several thousands of these patients.”15

He went on to lead a randomised trial. Unfortunately, the large effect found was an 80% increase in mortality.16


  • Competing interests: Both authors have read and understood BMJ policy on declaration of interests and have no relevant interests to declare.

  • Provenance and peer review: Commissioned; not externally peer reviewed.


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