Extraordinary claims require extraordinary evidence.--Carl Sagan
The term “evidence” has slightly different shades of meaning, depending on who uses it and for what purpose.
For example, courts of law have very strict rules about what types of facts and findings constitute sufficient legal evidence to justify taking away a person's freedom in a criminal trial.
Social science disciplines such as anthropology, sociology, and history, which can't, for the most part, use controlled experiments, also use the term in ways particularly suited to their own fields.
Natural science disciplines such as biology, chemistry, and physics, have the ability, in many cases, to run controlled studies to test ideas, and the results of those studies add to their body of evidence.
For that reason, so that we can communicate with each other, and with clients, and with healthcare providers and other stakeholders of massage about what we do and don't know, it is very important to establish what evidence means in our contexts most deeply involved with massage. Let's do that by building on the work we have already done up to this point.
As we've discussed, a claim is a statement that proposes the existence of a relationship between a treatment and an outcome.
Until a claim is tested (validated) to determine how correct or incorrect it is, that claim is usually considered to be unvalidated, or neutral, unless there are other very good reasons to treat it differently.
Evidence, for our operational definition here at POEM, consists of the cumulative body of facts, data, or information that result when claims are tested empirically for their correctness or incorrectness in the material physical universe.
Sagan’s quote at the beginning of this section highlights the fact that we evaluate claims in that way within the whole integrated framework of our cumulative shared existing knowledge.
For example, if someone made a claim that
massage lowers high blood pressure in heart patients with dangerously high blood pressure
that claim would not be considered particularly extraordinary, because there is already a body of evidence supporting the idea that massage lowers blood pressure in people with a variety of conditions.
This new claim fits with what has already been tested and demonstrated on a number of occasions. So while this particular novel claim would still be treated as unvalidated until someone actually tests it to determine how well it reflects reality, it is not an especially extraordinary claim, in light of the existing evidence already available.
On the other hand, if someone were to make a claim such as
massage can cure rabies in children
that claim, in light of what is known both about massage and about infectious disease, would be quite extraordinary.
Rabies is a disease caused by a virus that attacks the brain, and without pharmacological treatment for infected victims before symptoms appear, it's virtually 100% fatal, with a great deal of pain and distress before death.
Source: http://upload.wikimedia.org/wikipedia/commons/9/9f/Middle_Ages_rabid_dog.jpg accessed 4 May 2012
To claim that a noninvasive treatment such as massage can cure a fatal viral brain disease would require overturning a great deal of existing knowledge about massage, microbiology, and how the material physical universe operates--meaning that much or all of the previous evidence gathered would have to be shown to have been in error all along.
To claim that would also be a clear statement that, to the claimer, massage has no intention of integrating with the shared body of knowledge of healthcare professions--to reject that body of knowledge as strongly and unambiguously as this claim does would present an obstacle to integration into a client-centered healthcare team, unified through that body of knowledge.
Of course, that only applies if it were really a serious claim, not just a made-up example, as this one is--but there are a large number of extraordinary claims routinely made about massage that present just such obstacles to integration, and we'll talk about them as they come up in the discussion.
The evidentiary burden (burden of proof) of this extraordinary claim is much higher than the previous one about blood pressure--not only does it have to demonstrate its own validity, but it also has to account for why so many observers have been wrong about so many other interconnected questions over so many centuries.
This rarely happens in science, and when it does happen, it is almost always in domains that are new and still poorly understood--"frontier science", as it's often called. And it's even rare in frontier science; what happens there much more often is that ideas that initially looked promising don't survive the scrutiny of thorough testing.
For something that we already understand as well as we understand infectious disease, we don't need to take this particular claim seriously. We are justified in rejecting the claim "massage cures rabies in children" without doing the work of subjecting it to rigorous clinical trials before we make up our minds.
Multiple lines of evidence across many centuries in many places around the world have produced a body of evidence that is very strong, and the claim has such a huge evidentiary burden to overcome to replace all that evidence, that it is extremely unlikely--effectively impossible--that the claim will meet its burden of proof.
For more thoroughly studied areas of inquiry--what's often called "textbook science" or "consensus science"--the more typical outcome resembles the results of Einstein’s theories of relativity.
Although his ideas drastically changed how we view the universe, they did not actually replace previous knowledge so much as build a whole new area of knowledge on top of it—much like how adding a jet engine to a skateboard would radically change what the skateboard would be able to do but would not change what we already know about ordinary skateboards.
Source: http://www.youtube.com/watch?v=LPnHr_SxkRU accessed 4 May 2012
One day, extraordinary evidence might conceivably be gathered that would support some particular extraordinary claim--but to do so will always be a very tall order, in light of what the body of existing evidence and knowledge indicates.
Science is almost never a totally all-or-nothing proposition; rather, it all comes down to the overall strength of the facts taken in combination and how well this combination supports--or does not support--a given claim.
In this way, judging what counts as evidence is not only a function of how valid each single piece of evidence might be, but it is also a function of how well each piece of evidence fits with every other piece.
Scientific knowledge is considered provisional and contingent—it is always subject to being replaced later, if new and better evidence warrants the replacement. But until such a replacement occurs, any particular piece of scientific knowledge is considered to be good enough, for now--as long as the cumulative body of validated and shared evidence, built by a community of people working with a shared commitment to the integrity of the process, supports it.
(By "good enough", we mean only "good enough to meet the standard of evidence that we are comparing it to in the lack of absolute perfectly certain knowledge that we find ourselves having to operate in". We don't mean "good enough for the client" at all--one of the worst and most helpless feelings there is is to have to tell a suffering fellow human being "we truly don't know how to help you". In that sense, as long as people and animals are suffering in ways that we don't understand, our knowledge will never, ever be "good enough".)