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The Evidence Hierarchy Evolving

By now, we have all been exposed to the evidence pyramid. This is a graphic that demonstrates the apparen6t hierarchy of scientific papers, with those with the least rigor located at the bottom of the pyramid, and those with the most at the top. So, we have anecdote and case reports located near bottom, and as we move up the pyramid, we will find case-control studies and cohort studies, with randomized trials above them, and with systematic reviews and meta-analyses at the very top. Conceptually, this is meant to suggest that we should nearly always use information drawn from papers nearer the top of the pyramid. This way, we ensure that we are using the strongest evidence. But this can be challenged on a number of grounds. One is that sometimes a paper lower in the hierarchy is actually stronger than one higher, on methodological grounds. Clearly, not all published papers, of any type, are good. Second, as is the case in chiropractic, we often do not have higher-level papers for some of what we do. There are no hard trials of the use of manipulation for knee problems, for example. But we still treat knee pain.

There have been attempts to recalibrate this pyramid. One of the first was by Wayne Jonas, former director of NCCAM (now NCCIH) and director of the Samuelli Institute. Wayne formulated the “evidence house.” (1) He proposed that there be “rooms” for different kinds of information and purposes. These rooms could be used to look at relations between interventions and outcomes, or could later be used to make decisions in the real world of clinical practice. In each case, he was matching a specific need to a specific use and a specific audience.

A new paper has just come out as an editorial in the Journal of Clinical Epidemiology. (2) Their approach takes into account he possibility of selection bias (non-reporting of clinical information) and notes that there are growing problems in applying the hierarchy approach to complex clinical situations. They suggest a “circle of methods” as a means to look at information. I call this the evidence donut, for want of a better term. In the circle, there are four core elements: efficacy, comparative effectiveness, effects and safety, and effectiveness. To each are matched different kinds of papers, each specific for the kind of question asked.

These are questions about nosology, or naming, if you will. What this demonstrates is that evidence-based practice is growing and changing, and we can never get too complacent. It is a good thing.


  1. Jonas WB. The evidence house: how to build an inclusive base for complementary medicine. West J Med 2001;175:79-80
  2. Tugwell P, Knotterus JA. Editorial: Is the “evidence-pyramid” now dead? J Clin Epidemiol 2015;68:1247-1250


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