by Steven Novella via Skepticblog

Six years ago I was asked to participate in a group debate over the legitimacy of homeopathy at the University of CT (there were six speakers, three on each side). This year I was asked to participate in another homeopathy debate at UCONN, but this time one-on-one with Andre Saine ND from the Canadian Academy of Homeopathy taking the pro-homeopathy side. (I will provide a link when the video is posted online.)

While the basic facts of homeopathy have not changed in the past six years, the details and some of the specific arguments of the homeopaths have evolved, so it was good to get updated on what they are saying today. In this post I will discuss some overall patterns in the logic used to defend homeopathy and then discuss the debate over plausibility. In tomorrow’s post I will then discuss the clinical evidence, with some final overall analysis.

Believers and Skeptics

As with the last debate, the audience this time was packed with homeopaths and homeopathy proponents. When I was introduced as the president of the New England Skeptical Society, in fact, laughter erupted from the audience. But that’s alright – I like a challenge. It did not surprise me that the audience, and my opponent, were unfamiliar with basic skeptical principles. Andre, in fact, used the word “skeptic” as a pejorative throughout his presentation.

The difference in our two positions, in fact, can be summarized as follows: Andre Saine accepts a very low standard of scientific evidence (at least with homeopathy, but probably generally given that he is a naturopath), whereas I, skeptics, and the scientific community generally require a more rigorous standard.

The basic pattern of Andre’s talk was to quote from one of my articles on homeopathy declaring some negative statement about homeopathy, and then to counter that statement with a reference to scientific evidence. The problem is, his references were to low-grade preliminary evidence, and never to solid reproducible evidence.

That is one functional difference between skeptics and believers – the threshold at which they consider scientific evidence to be credible and compelling (there are many reasons behind that difference, but that is the end result).

I was asked what level of evidence I would find convincing, and that’s an easy question to answer because skeptics spend a great deal of time exploring that very question. In fact, I have discussed this in the context of many things, not just homeopathy.

For any scientific claim (regardless of plausibility) scientific evidence is considered well-established when it simultaneously (that’s critical) fulfills the following four criteria:

1. Methodologically rigorous, properly blinded, and sufficiently powered studies that adequately define and control for the variables of interest (confirmed by surviving peer-review and post-publication analysis).
2. Positive results that are statistically significant.
3. A reasonable signal to noise ratio (clinically significant for medical studies, or generally well within our ability to confidently detect).
4. Independently reproducible. No matter who repeats the experiment, the effect is reliably detected.

This pattern of compelling evidence does not exist for ESP, acupuncture, any form of energy medicine, cold fusion or free energy claims, nor homeopathy. You may get one or two of those things, but never all four together. You do hear many excuses (special pleading) for why such evidence does not exist, but never the evidence itself.

The reason for this is simple – when you set the threshold any lower, you end up prematurely accepting claims that turn out not to be true.

Plausibility

The less plausible, the more outrageous and unconventional a scientific claim, the more nitpicky and uncompromising we should be in applying the standards above. This follows a Bayesian logic – you are not beginning with a blank slate, as if we have no prior knowledge, but rather are starting with existing well-established science and then extending that knowledge further.

To clarify – if a new claim seems implausible it does not mean that it is a-priori not true. It simply means that the threshold of evidence required to conclude that it is probably true is higher.

Scottish philosopher David Hume sort of captured this idea over two centuries ago when he wrote:

No testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous than the fact which it endeavors to establish.

I like to think of it this way: The evidence for any new claim that contradicts prior established scientific conclusions must be at least as robust as the prior evidence it would overturn. You can also ask the question – what is more likely, that the relevant scientific facts are wrong, or that the new claim is wrong?

What is more likely, that much of what we think we know about physics, chemistry, biology, physiology, and medicine is wrong, or that the claims of homeopathy are wrong? I think this is an easy one.

MORE . . . Debating Homeopathy Part I

• Debating Homeopathy Part II

Related articles

• Debating Homeopathy Part I (skepticblog.org)
• Keeping Up the Pressure (illuminutti.com)
• Teaching Chemistry With Homeopathy (randi.org)
• Keeping Up the Pressure (randi.org)
• Debating Homeopathy Part I (theness.com)
• Debating Homeopathy Part II (theness.com)
• What is Homeopathy? (nomadicvet.wordpress.com)
• Evidence Thresholds (sciencebasedmedicine.org)
• HumanistLife : Homeopathy – Faith or Science (humanistlife.org.uk)