How Strong is Your Evidence?

If you’ve had heart problems, chances are you’ve received some advice from your doctor on how best to care for your condition. Maybe you were advised to take an aspirin daily, exercise regularly, or cut down on the salt in your diet. Maybe you were handed a sheaf of prescriptions bearing foreign-sounding medication names with the assurances that they would help stave off future problems. And if you’re like many patients, you took the doctor at his or her word, assuming he or she was acting based on sound medical evidence. Unfortunately, that assumption may have been false.

The push in medical education for several years has been towards more evidence-based medicine; that is, we should teach our young doctors to recommend to their patients what has been scientifically proven to be beneficial. However, a recent study published in the Journal of the American Medical Association (JAMA) found that, at least with regards to cardiovascular problems, the vast majority of the medical evidence supporting current recommendations is weak. Researchers examined the current recommendations of the American Heart Association and the American College of Cardiology on 22 different cardiovascular topics. They graded the strength of the evidence supporting these recommendations from A to C, with A being the best evidence, and C being very little or weak evidence. Only 12% of the recommendations were in the A category. A staggering 45% earned a C.

There are many potential reasons for this, not the least of which is simply the lack of powerful data. The ideal medical study is a large, multicenter, randomized, double-blind, controlled trial funded by an organization with no vested interest in the outcome. The closer a study comes to this ideal, the stronger the evidence is to support its findings. However, many studies fall short of this ideal on numerous fronts. They involve a small or restricted subgroup of patients. They’re performed at only one medical center. They’re funded by the company that makes the medication or device being studied. Any of these shortcomings call the results of the study into question and weakens the strength of the evidence. Can these findings be applied to a larger or less restricted population? Can the results be reproduced at a different hospital? Are the researchers biased towards finding a positive outcome for the company that funds their research?

So should you ignore the majority of what your doctor says for lack of strong evidence? Not necessarily. Most doctors are simply working with the best information they have, even if the data supporting it is weak. What studies like this highlight is the need for better research to ensure that our recommendations are based on sound scientific evidence.


P. Tricoci, J. M. Allen, J. M. Kramer, R. M. Califf, S. C. Smith (2009). Scientific Evidence Underlying the ACC/AHA Clinical Practice Guidelines JAMA: The Journal of the American Medical Association, 301 (8), 831-841 DOI: 10.1001/jama.2009.205

T. A. McNamee, MD

T. A. McNamee, MD, is an associate professor and internal medicine residency program director at Sanford School of Medicine of the University of South Dakota.
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