The Philosophy of Evidence-Based Medicine by Jeremy Howick (review)

The idea that prescribing physicians should be guided by the most reliable scientific evidence seems obvious, but the actual methodology of evidence-based medicine was only introduced in the early 1990s by an international group of clinicians and researchers led by Gordon Guyatt. Since then it has provided a new paradigm for the scientific foundation of medicine and has influenced other disciplines outside of medicine, for example, evidence-based psychotherapy, science and government. The novel concept of evidence-based medicine is based on hierarchies of evidence from opinions of respected authorities, mechanistic reasoning (pathophysiologic rationale), and reports of expert committees at the bottom to various levels of observational studies and finally to randomized clinical trials (RCTs) at the apex of the pyramid. Since RCTs provide the most rigorous testing of therapies, they are the gold standard. When treatments long believed to be safe and effective are subjected to RCTs, many turn out to be as useless as the quackery of snake oil or as harmful as mercury. So, attention to RCTs as the evidence informing clinical judgment and practice is perhaps analogous to results of rigorous experiments in physics which turn out to be very different from our intuitions. Everyone, it seems, is on the bandwagon, from medical societies and pharmaceutical companies to general practitioners and surgeons, in the quest for an evidence-based practice.

Since evidence-based medicine was conceived with the practical aim of improving the efficacy of medicine, it does not appear that there is much of philosophical interest in the concept until one raises the epistemological question, as Jeremy Howick does in this book: What is the evidence for evidence-based medicine philosophy of evidence (9)? In other words, what is the evidence that evidence-based medicine is any better in improving patient outcomes than medical practice before the new paradigm? So, evidence-based medicine requires evidence and this is what Howick attempts to achieve in this splendid treatment of the subject. With an eye on the philosophical, Howick is also concerned with various paradoxes that [End Page E-1] arise concerning the hierarchies of evidence-based medicine; for example, many treatments in whose effectiveness we have the most confidence have never been subjected to RCTs, including simple procedures such as the Heimlich maneuver and tracheotomy. Howick’s thesis is that the evidence-based medicine hierarchies are sustainable provided that we take into account certain modifications, for one that “strict hierarchies should be replaced by the requirement that all evidence of sufficiently high quality should be admitted as evidential support” (xiv, 187). This being the case, we need not subject treatments we know to be effective to RCTs, for this would be as redundant as the need to test parachute effectiveness against parachute placebo.

In order to qualify as good evidence for an evidence-based medicine, outcomes must be clinically effective (clinically significant, rather than merely statistically significant) according to which: (i) patient-relevant benefits outweigh any harms, (ii) the treatment is applicable to the patient being treated, and (iii) it is the best available option (24). The evidence must demonstrate that the patient will live longer or better. Good evidence also rules out plausible rival hypotheses (33). So, RCTs generally maintain their position in the hierarchies because when well-designed and well-conducted (double-masked and randomized), RCTs minimize confounding factors such as the expectation of patients to recover by knowing they are given the experimental treatment. Observational studies cannot meet this standard because they involve observations in routine practice that cannot rule out the confounding factors. Certain observational studies will claim a treatment to be effective and safe but, when subjected to rigorous RCTs, show the very opposite. The same relationship holds between conclusions drawn on the basis of mechanistic reasoning and well-conducted clinical studies. Faced with contradictory conclusions from results in the hierarchies, Howick says it is rational to bet on the results form RCTs since RCTs are less likely to suffer from bias (53).

However, Howick introduces his rule of evidence: comparative clinical studies (or observational studies...