On November 1, 2023, from 6 to 7 p.m. at the Redpath Museum Amphitheatre, Gordon Guyatt, MD, Distinguished Professor in the Departments of Medicine and Health Research Methods, Evidence & Impact at McMaster University, will deliver the 2023 Osler Lectureship, “How evidence-based medicine has – and has not – changed the world.” Ahead of his visit, Todd Meyers, PhD, from the Department of Social Studies of Medicine, spoke with Dr. Guyatt about his pioneering work in evidence-based medicine.   

Todd Meyers (TM): The big question is, what is the “evidence” in evidence-based medicine (EBM)?  What exactly was EBM trying to capture at the time it was introduced and has that changed over the years? 

Gordon Guyatt (GG): There are three principles that define EBM. First is that some evidence is more trustworthy than others. Second is that to make optimal health care decisions, one needs systematic reviews, because if you don’t have it all there, you pick and choose and that’s problematic.  And third is that evidence itself never makes decisions.  Evidence is always in the context of values and preferences.   

At the beginning, we knew that some evidence was more trustworthy than others, but we didn’t have a great system for deciding.  We did not emphasize the need for systematic reviews in the Journal of the American Medical Association (JAMA) publication that made such a splash.1 Systematic reviews were not as well established as they became and there was no hint of anything about values and preferences.  A few years later the penny had dropped, and we began to address values and preferences.  And then in 2000, we explicitly said, “evidence never makes decisions by itself,” but despite this fact you still see criticisms of EBM as if we have not been shouting this for the last 23 years about the importance of values and preferences. 

TM: What were the origins of the EBM approach at McMaster University?  Perhaps the intellectual influences, personalities, political conditions in that place at the time?

GG: A history PhD student who, unfortunately, never published his book focused on this moment at McMaster, suggested in the late 1980s the authority of the medical establishment was being challenged in a way that it had not before and thus EBM was medicine’s attempt to re-establish the authority that was being threatened.  I have no idea whether that’s true or not.  But it is remarkable how quickly EBM was picked up. Something was right at the time.    

I suspect medical students or even some of my junior colleagues, if you ask them, “when did EBM arise?” would probably say about 1880!  But around 1980, one of my mentors, Dave Sackett, got the idea that clinicians should be taught to read the methods and results of articles that might inform practice.  This was something new.  He started to teach what he called “critical appraisal.” It was a classroom activity, but then a number of us in parallel started to apply this in our day-to-day clinical practice — what Dave called “bringing critical appraisal to the bedside.”  This was a profoundly different way of practising medicine.  In 1990, I became the director of the internal medicine residency program at McMaster with a mandate to realize this different way of practising. But what to call it?  My first idea was “scientific medicine,” but when I introduced this to my department filled with basic scientists, the outrage was very intense.  My next suggestion, which was EBM, proved to be a big hit. I published a single author paper in 1991, the first time EBM appears in the medical literature.  Nobody noticed that one, but in 1992, the JAMA paper established the idea. Two years later, I received promotional literature from the American College of Physicians that started, “in this era of evidence-based medicine…,” which was extraordinary.  I don’t know if the historian is right, but there was something in the socio-political environment that led to this reception.  

TM: Would you talk a little more about the impact of your landmark 1992 JAMA paper?  How surprised were you by the reception? 

GG: Perhaps we were arrogant enough to not have been as surprised as we should have been. We were certainly surprised, but I’m thinking now in retrospect, we should have been really surprised. People said, “oh, we’ve got to teach this,” so very quickly it was now a new addition to the undergraduate medical and residency curriculum. In my seven years as director of the McMaster internal medicine residency program, I made it my goal to ensure my residents were able to read the methods and results of primary literature and systematic reviews, and able to critique these papers in order to make their own decisions.  But at the end of seven years, it was evident that this was not going to happen.  Shortly after I finished my stint as director of the residency program, we published a paper saying EBM should be part of the curriculum but doctors can’t be expected to do the critical appraisal themselves. They need to know the implications of variable quality evidence, whether it’s high or low quality. They need to know when we know and when we don’t know.  And they need to be able to understand the magnitude of benefits and harms and burdens that patients face in order to engage in shared decision making with patients. 

TM: In your JAMA, papers you describe EBM as a “new paradigm” for medicine.  As with every paradigm shift, there are critics.  The most common critiques of EBM suggest that the approach is too simplistic methodologically or that clinical trials are themselves not unproblematic and thus do not always provide truly useful data.  I’m curious how criticism has shaped your thinking or rethinking of EBM along the way?

GG: As far as I can tell, the critiques come out of failure to read what we actually write. 

As early as 2000 we said a key principle of EBM is evidence never makes the decisions, but you still see people writing as if we are saying that evidence makes decisions. In 2004 we published a paper in the British Medical Journal2, and it said that although randomized trials by their nature yield higher quality evidence than observational studies, that comes with a lot of provisos. There’s risk of bias, there’s imprecision, there’s inconsistency, there’s indirectness, there’s publication bias, and even if you have randomization, it may end up as low or very low-quality evidence. On the other hand, although observational studies usually yield a lower quality of evidence, we know that hip replacements are a great thing for hip osteoarthritis and insulin is a great thing for diabetic ketoacidosis and renal replacement therapy is a great thing for people with renal failure, and we know all this without randomized trials. So, there are instances when there are large or very large effects where we have high certainty evidence without randomized trials.  EBM has become a much more sophisticated approach that recognizes the limitations of randomized trials and recognizes situations in which non-randomized studies can yield high certainty evidence.  If the critics say EBM is all about randomized trials, they haven’t been reading what we’ve been writing since at least 2004. 

TM: What do you see as the place of EBM going forward in terms of health education and care?

GG:  There is still work.  We need to do a better job of getting people to understand the certainty of evidence, and understanding the magnitude of benefits and downsides. And for this, we need to improve ways of presenting data.  We need to optimize clinical practice guidelines. And we need to get better at helping people to do shared decision-making efficiently.  

The 46th Annual Osler Lectureship with Gordon Guyatt takes place on November 1 at the Redpath Museum Auditorium. Full info. 

  1. Evidence Based Medicine Working Group; Guyatt G, Cairns J, Churchill D, et al. Evidence-Based Medicine Working Group. “Evidence-based medicine. A new approach to teaching the practice of medicine.” JAMA vol. 268,17 (1992): 2420-5. doi:10.1001/jama.1992.03490170092032
  2. Guyatt G, Cook D, Haynes B. Evidence based medicine has come a long way. BMJ 2004 Oct 30;329(7473):990-1. doi: 10.1136/bmj.329.7473.990.