The fundamental concept of science-based medicine (SBM) is that medical practice should be based upon the best available science. This may seem obvious, but there are many important details to its application, such as the relationship between clinical and basic science. Clinical claims require clinical evidence, but clinical evidence can be tricky and is often preliminary. It is therefore helpful (I would say essential) to view the clinical evidence in light of all of the rest of science.
A thorough basic and clinical science analysis of a medical claim can be summarized by the term “plausibility,” or “prior probability” if you want to put it into statistical terms. When we say a certain belief is plausible we mean it is consistent with what we know from the rest of science. In other words, because of the many weaknesses of clinical evidence, in order for a therapy to be generally accepted as part of SBM it should have a certain minimal supporting clinical evidence and overall scientific plausibility.
These can exist in different proportions – for example one therapy may be highly plausible (it would be shocking if it were not true) and have modest supporting clinical evidence, while another may have unknown plausibility but with solid clinical evidence of efficacy. But no therapy should have clinical evidence that suggests lack of efficacy, nor extreme implausibility (not just an unknown mechanism, but no possible mechanism).
A question that arises often when discussing the optimal role of science in medicine is the precise role of plausibility, or prior probability. This is, in fact, the central concept that separates (for practical if not philosophical reasons) science-based medicine (SBM) from evidence-based medicine (EBM).
The concept featured prominently in the debate between myself and Dr. Katz at the recent Yale symposium that Kimball Atwood recently discussed. Dr. Katz’s treatment of the topic was fairly typical of CAM proponents, and consisted of a number of straw man derived from a false dichotomy, which I will describe in detail below.
I also recently received (I think by coincidence) the following question from an interested SBM reader:
What would Science Based Medicine do if H. pylori was not known, but a study showed that antibiotics given to patients with stomach ulcers eliminated symptoms? I assume that SBM wouldn’t dismiss it outright saying that it couldn’t possibly be helping because antibiotics don’t reduce stomach acid. I assume a SBM approach would do further studies trying to discover why antibiotics work. But, in the meantime, would a SBM practitioner refuse to give antibiotics to patients because he doesn’t have a scientific explanation as to why it works?
This is the exact type of scenario raised by David Katz during our discussion. He claimed that strict adherence to the principles of SBM would deprive patients of effective treatments, simply because we did not understand how they work. This is a pernicious straw man that significantly misconstrues the nature of plausibility and its relationship to the practice of medicine.
In part 2 of the Science-Based Medicine 101 series we take a look at the second pillar of good science: plausibility. This blog post was written for a lay audience so more advanced readers will need to indulge me here…
I really enjoy sci-fi action movies. I love the convincing special effects and the fact that heroes can accomplish the physically impossible without skipping a beat. Implausible events unfurl with convincing reality, and you never know what might happen with the plot.
I also enjoy the TV show, America’s Funniest Home Videos, for different reasons. The mundane nature of actual reality, and the often predictable, but hilarious mistakes made by those I relate to result in some pretty hearty laughs.
But there is a big difference between these two forms of entertainment: science-fiction requires the suspension of belief in plausibility, while home videos are based on plausible outcomes. When it comes to medical research, though, plausibility can mean the difference between science fiction and reality.
Most scientific research studies have at least one thing in common: the conclusion section ends with, “further research is warranted.” I’d say it’s about as common as the “talk to your doctor” disclaimer in TV ads for pharmaceutical products. And in a way, they both serve the same purpose. They’re a “CYA” move.
What does “further research is warranted” mean in plain English? I think it can be roughly translated: “My research study is not of the size or scope to fully explain all the phenomena described in this article. Therefore, draw conclusions beyond the data and study methods at your own risk. And yeah, my work is important and cool – so people should study it further.”
Of course, the first two sentences are reasonable – we should always remember not to draw conclusions beyond the information provided by the data we’ve collected (even though that’s about as challenging as getting a beagle not to eat a table scrap in an empty room). The real problem is the third sentence. Is the research promising enough to require further investment? How are we to know if further research is indeed warranted? I would argue that it should not be based solely on the subjective opinions of the researchers nor the popularity of the research topic to the general public. (more…)