From the very outset, the founders of Science Based Medicine have have emphasized the importance of plausibility in the critical evaluation of scientific claims in medicine. What exactly does “plausibility” mean, and how should we apply it in science? My simple definition of plausibility would be “the likelihood that a premise is true.” The application in science is a little more complicated.
Consciously or unconsciously, we all consider plausibility in interpreting events in our lives. For example, if one of your coworkers showed up late for work and grumbled about a traffic jam, you would likely accept his story without question. If, instead, the same coworker attributed his tardiness to an alien abduction, you would not be so charitable. In each case, he has provided the same level of evidence: his anecdotal account. You are likely to accept one story and reject the other because of a perceived difference in the plausibility. The skeptic’s mantra “Extraordinary Claims Require Extraordinary Evidence” expresses this concept in a qualitative way.
Evidence-based medicine has traditionally ignored plausibility when interpreting the evidence for a medical intervention. Science-based medicine, as envisioned by the creators of this blog, includes plausibility when making these judgements.
Since experiment research employs rigorous controls, and statistical criteria, you might assume that plausibility is not an issue, however, this is not entirely true. An article written by John Ioannidis entitled “Why Most Published Research Findings Are False” is cited frequently as a reference for the impact of plausibility on the interpretation of research results. This article enumerates numerous factor leading to erroneous research conclusions. Most of them have been dealt with on this blog at one time or another. To me, the most eye-opening aspect of the paper was a quantitive approach to the influence of plausibility in interpreting positive research findings. I was never taught this approach in medical school, or in any other venue. When it comes to implausible hypotheses, the traditional P-value can be very misleading.
As good as Ioannidis’ article is, it is not easy reading for the statistically or mathematically challenged. What I attempt to do in this post is to demonstrate the importance of plausibility in graphic format, without a lot of complex math. If you can grasp the concepts in this post, you will have an understanding that many researchers, and consumers of research, lack.