The problem of bias, both subconscious and conscious, in medical research was a consistent theme through many of the talks delivered at Evidence Live this year. As the first post in a series on the talks from Evidence Live, this article will give an overview of what evidence based medicine actually is. In his session, Dr David Nunan explored the top 10 papers explaining the practice of evidence-based medicine (EBM), an approach developed to combat the harms caused by biased research. Each of of these papers is listed at the bottom of this article.

Dr Nunan is lead author on a paper published in BMJ Evidence-Based Medicine which sets out the basics of EBM as an introduction for those unfamiliar with it. The basic goal of the paper was to address a few basic questions about EBM: What problems prompted EBMs development? What is EBM? What are the problems with EBM? How should one go about practising EBM?

In answer to the first question, Dr Nunan raised the example of flecainide and the dangers of a ‘mechanistic approach’ to using evidence. The drug was being used to treat arrhythmia in patients in the USA throughout the 1980s, but the evidence supporting its use was not comprehensive: the trial it was based on had a cohort of only 10 patients who had previously experienced a heart attack, whose rate of irregular contractions over the course of 2 weeks was monitored. Although this study suggested that flecainide could reduce the number of irregular contractions in patients, it only looked at a short time frame and had too small a sample size to offer definitive proof. Nevertheless, flecainide was approved for arrhythmia as an indication by the Food and Drug Administration (FDA), and by 1989, 200 000 patients had been prescribed the drug following a heart attack.

Flecainide turned out not to be so beneficial as initially thought. A randomized controlled trial (RCT) in 1991 with 1496 participants and a follow-up period of 10 months found that, on average, three times as many patients taking flecainide following a heart attack died compared with those who received placebo.

This is a troubling case study – but how does EBM prevent cases like this from happening again? The answer to this was suggested in paper number one: ‘Evidence-based medicine. A new approach to teaching the practice of medicine’, which was published in JAMA in 1992. The paper stated that the aim of EBM is to “de-emphasize … intuition [and] unsystematic clinical experience … as sufficient grounds for clinical decision making” and that it also “requires new skills of the physician, including efficient literature searching and the application of formal rules of evidence evaluating the clinical literature”.

To achieve this, EBM’s proponents developed the five As: ask a well-formulated clinical question, acquire the best evidence, appraise the evidence, apply the evidence, and then assess the impact and performance of that application.

It is important to note, however, that there has been criticism of EBM as a discipline, which was explored as a part of Dr Nunan’s talk. The featured criticism in the paper was a systematic review on EBM, written by Sharon Straus and published in CMAJ in 2000, entitled ‘Evidence-based medicine: a commentary on common criticisms’. The paper outlined three limitations of EBM: it takes time and resources, it requires new skills and, ironically, there is little empirical evidence as to whether the EBM approach improves practice. It also listed common misinterpretations, most prominently, the ‘ivory tower’ image of the proponents of EBM, who are often perceived as criticizing practitioners on the front lines of healthcare from the safety of academia. In reality, however, this perception does not seem to be shared by the majority of primary care physicians. In a survey conducted by the Centre for Evidence-Based Medicine, the majority of the 302 general practitioners surveyed thought that an EBM approach improved patient care.

In the years since EBM was first proposed in the early 1990s, access to evidence for doctors has increased dramatically. The vast majority of doctors now have access to the Internet, and a huge variety of resources are now available through it. Therefore, doctors have the opportunity to access and use evidence in a way that was not feasible in the past. This means that the time is ripe for the proliferation of EBM in practice.

The list of papers selected by Nunan in his paper as the key primers on Evidence Based Medicine are listed below.
1. Sackett DL, Rosenberg WMC, Gray JAM et al. Evidence based medicine: what it is and what it isn’t. BMJ 1996;312:71-2. doi: 10.1136/bmj.312.7023.71
2. Guyatt G, Cairns J, Churchill D et al. Evidence-based medicine: A new approach to teaching the practice of medicine. JAMA 1992;268:2420-5. doi: 10.1001/jama.1992.03490170092032
3. Altman DG. The scandal of poor medical research. BMJ 1994;308:283-4. doi: 10.1136/bmj.308.6924.283
4. Heneghan C, Mahtani KR, Goldacre B et al. Evidence based medicine manifesto for better healthcare. BMJ 2017;357 doi: 10.1136/bmj.j2973
5. Glasziou P, Vandenbroucke J, Chalmers I. Assessing the quality of research. BMJ 2004;328:39-41. doi: 10.1136/bmj.328.7430.39
6. Schulz KF, Chalmers I, Hayes RJ et al. Empirical evidence of bias: Dimensions of methodological quality associated with estimates of treatment effects in controlled trials. JAMA 1995;273:408-12. doi: 10.1001/jama.1995.03520290060030
7. Coomarasamy A, Khan KS. What is the evidence that postgraduate teaching in evidence based medicine changes anything? A systematic review. BMJ 2004;329:1017. doi: 10.1136/bmj.329.7473.1017
8. Straus SE, McAlister FA. Evidence-based medicine: a commentary on common criticisms. CMAJ 2000;163:837-41.
9. McColl A, Smith H, White P et al. General practitioners’ perceptions of the route to evidence based medicine: a questionnaire survey. BMJ 1998;316:361-5. doi: 10.1136/bmj.316.7128.361
10. Gabbay J, le May A. Evidence based guidelines or collectively constructed “mindlines?” Ethnographic study of knowledge management in primary care. BMJ : British Medical Journal 2004;329:1013.


One thought on “Evidence Live – what is evidence-based medicine?

Leave a Reply