A new perspective on evidence-based medicine

Meet the new Evidence-Based Medicine columnist for Veterinary Practice News

For years, I enjoyed Dr. Narda Robinson’s insightful and informative column in Veterinary Practice News. She tackled timely, complex and controversial subjects from a pragmatic, evidence-based perspective, and I found her assessments always interesting and useful. She has taken up other challenges, and as I follow in her footsteps, I hope to provide VPN readers with discussions of issues that clinicians in practice face every day.

An embarrassment of riches exists in veterinary medicine today in terms of the products, tools and techniques available to us and in terms of the volume of information we must wade through to provide guidance to our clients and effective, up-to-date treatment for our patients. Strolling through the exhibit hall at any major continuing education conference or perusing the pages of this magazine illustrates the abundance of claims we must evaluate as practitioners. My hope for this column is to use the principles and methods of evidence-based medicine to sort through these claims so that you more easily make choices for yourselves, your clients and your patients.

My perspective is that of a small animal veterinarian in private practice for more than 15 years. I see patients every day and face the same flood of information and options many of you face. Like you, I must choose among many diagnostic and treatment methods as well as educate and guide my clients, which often involves combating the profusion of misinformation so easily found online. For me, evidence-based medicine (EBM) is not a dry academic exercise but a practical tool for managing information and making decisions.

In the decade I studied and taught EBM, I developed an approach aimed specifically at practicing veterinarians. Those interested in greater detail can find out more about this approach in some of my published papers or conference presentations.1-3 For now, I will introduce the general steps I will follow in future columns to evaluate claims for specific tests or treatments.

The Evidence Pyramid

The traditional image associated with EBM is the evidence pyramid—a visual tool that ranks the reliability of different levels of evidence, usually from laboratory studies and expert opinion at the bottom to meta-analyses or systematic reviews at the top.

This graphic above is useful, albeit academic. Most of us don’t have the time or expertise to categorize articles we read by study design and critically evaluate their methodology. Therefore, my variation on this pyramid more easily helps me to structure the evidence I use to evaluate medical claims.

The pyramid represents the common types of evidence available to practitioners, and it illustrates the relative availability and reliability of different evidence. At the bottom is the most common and readily available evidence—our own opinions. These typically are based on our clinical experience, our school training and the opinions we have internalized from other people. Often, we don’t remember where particular beliefs or opinions originate, but they are easy to access and use in practice.

While no clinician could possibly practice without regularly relying on his or her existing knowledge and beliefs, it is important to remember these are at the bottom of the pyramid. For reasons I will reiterate repeatedly, we are wrong much more often than we realize. Evidence- based medicine exists and is useful precisely because it can help us to be wrong less often!

We in general practice are taught to defer to the expert opinion; however, it isn’t always clear who is truly an expert. Expertise might be signaled by something tangible, such as board certification in a specialty. Or a purported expert simply may be another veterinarian with experience or training we don’t have. Expert opinion is easy to access and often useful. Genuine experts with relevant scientific training and experience are likely to have greater familiarity with the scientific evidence in their area of expertise than those of us in general practice.

However, experts are human beings who suffer all the same sources of error as the rest of us. When their opinions are not founded on science but on personal experience, they are no more reliable than any uncontrolled observation, which places expert opinion near the bottom of the pyramid.

Cutting Through the Overwhelm

The largest source of evidence available is the primary research literature. However, the volume of published research in veterinary medicine is enormous. When we include relevant research in humans and laboratory animals, the amount of evidence on any given topic is often overwhelming. It is seldom practical for practicing veterinarians to search and review the primary literature every time they must make a clinical decision.

The most efficient and most reliable type of evidence— and also the scarcest—is at the top of the pyramid. The synthetic literature includes all those reviews of the primary literature that go beyond mere expert opinion to systematically identify and critically evaluate all the relevant scientific evidence. Critically appraised topics (CAT) and systematic reviews are convenient, reliable summaries of the evidence for busy clinicians.

Unfortunately, too few of these useful tools exist, but more are becoming available all the time. The VetSRev database lists all the published systematic reviews in veterinary medicine (http://webapps.nottingham .ac.uk/refbase/), and a growing number of useful CATs can be found online as well (e.g., bestbetsforvets.org, veterinaryevidence.org).

Clinical guidelines also can be extremely useful. One must be wary, though, of those that are not truly evidence based but simply a repackaged expert opinion. The Reassessment Campaign on Veterinary Resuscitation (RECOVER) CPR guidelines are a great example of genuine evidence-based clinical practice guidelines.4

A Systematic Approach

When I evaluate a medical claim, I use these types of evidence. I start at the top, looking for the most reliable evidence, and I work down the pyramid to determine a comprehensive, objective overview of the science behind the claim. Inevitably, there will be gaps in the evidence and uncertainty. All too often, I must rely more on opinion and experience and less on controlled research evidence than I would like. But as a clinician, I make decisions on the basis of the best evidence available, not the perfect evidence I wish I had.

In my column, I will use this approach to review new products and discoveries, traditional and unconventional treatments, and common myths or misconceptions owners and veterinarians may have. After reviewing the evidence and considering its limitations, I will try to provide a clear bottom line, identifying how reliable each claim is and whether we should consider incorporating it into our practice.

I look forward to using the powerful tool of evidence-based medicine to help you sort through the flood of available information so that you can make the best decisions for your patients and give confident, science-based guidance to your clients.


  1. McKenzie BA. “Evidence-based veterinary medicine: What is it and why does it matter?” Equine Vet Edu. 2014; 26(9):451-452.
  2. McKenzie BA. “Veterinary clinical decision-making: cognitive biases, external constraints, and strategies for improvement.” J Amer Vet Med Assoc. 2014; 244(3):271-276.
  3. McKenzie BA. “EBVM in the Trenches: Pragmatic Strategies for Implementing EBVM in General Practice.” EBVM 2014: 1st International Evidence- based Veterinary Medicine Network Conference, Windsor, U.K., October 2014. [Video file]. Retrieved from youtube.com/watch?v=DC2ULW9vpws.
  4. Fletcher DJ, Boller M, Brainard BM, et al. “RECOVER evidence and knowledge gap analysis on veterinary CPR. Part 7: Clinical guidelines.” J Vet Emerg Crit Care (San Antonio). 2012 Jun; 22 Suppl 1:S102-31.

After earning his bachelor’s at the University of California, Santa Cruz, Dr. McKenzie obtained a master’s in physiology and animal behavior, and worked for several years in environmental and behavioral enrichment for captive primates. After attending the University of Pennsylvania School of Veterinary Medicine, he began working as a small animal general practice veterinarian. In the course of trying to improve his knowledge and better educate his clients, he discovered evidence- based veterinary medicine. Since then, he has served as president of the Evidence-Based Veterinary Medicine Association (EBVMA) and has reached out to the public through his SkeptVet Blog and his contributions to the Science- Based Medicine Blog and media interviews on veterinary medical topics. He earned his MSc in epidemiology at the London School of Hygiene and Tropical Medicine in 2015, and is certified in medical acupuncture for veterinarians. In his free time, he enjoys reading, hiking, playing his mandolin, traveling with his family and sitting on the couch with his dogs watching the hummingbirds and woodpeckers outside his living room window.

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