Science denialism and the evidence double standard


Science denialists have a deeply fraught relationship with scientific evidence. On the one hand, even the most outlandish forms of denialism attempt to invoke the imprimatur of science. Claims range from the simple (“studies show …”) to the elaborate (lists of scientific citations of papers that appear to support the claims being advanced, but actually do not). On the other hand, when scientific evidence undermines their claims, denialists suddenly discover that scientific evidence is not “applicable” to their claims or is “not enough” or produced by scientists with ostensible financial conflicts of interest.

Denialists use science only when it supports their pre-determined conclusions.

As Professor Rory Coker explains:

Pseudoscience appeals to the truth-criteria of scientific methodology while simultaneously denying their validity. Thus, a procedurally invalid experiment which seems to show that astrology works is advanced as “proof” that astrology is correct, while thousands of procedurally sound experiments that show it does not work are ignored…

Something similar plays out in every type of science denialism. Consider anti-vaccine advocacy. On the one hand, antivaxxers brandish scientific papers that show deleterious effects of various vaccine components like thimerosol or aluminum. Leaving aside for the moment that the papers are typically not directly relevant (involving related but different chemicals, involving massive amounts as compared to the minuscule amounts present in vaccines), these are real scientific papers containing valid scientific evidence.

But, unfortunately for anti-vaxxers, there are tens of thousands of scientific papers that demonstrate the safety and efficacy of vaccines. In contrast to the scientific papers that they like, this mass of scientific research, is not accepted on its face. When trying to persuade the unsophisticated, scientific evidence is explicitly rejected (“vaccine preventable diseases were decreasing BEFORE vaccines were invented”). If the audience is more sophisticated, a more subtle approach is required. In that case, specific poorly done papers are critiqued, never mind that they aren’t particularly representative of the literature as a whole.

This double standard is deftly summarized by Edzard Ernst MD, PhD, FMedSci, FSB, FRCP, FRCPEd in a brief editorial in the journal he edits, Focus on Alternative and Complementary Therapies (FACT). Prof. Ernst is the bete noire of “alternative” health. His credentials are impeccable. He was the first Professor of Complementary Medicine in the UK. Born and trained in Germany, he began his career at a homeopathic hospital. His belief in “alternative” health was so complete, he set out to show that its various remedies are both safe and effective.

But what he found apparently shook him to the core. His 700 published papers represent a lifetime of research that led him to conclude that only 5% of “alternative” medicine is backed by scientific evidence. The other 95% has either not been studied or has been definitely shown to be ineffective, unsafe, or both. Not surprisingly, Dr. Ernst is now viewed as “the scourge of alternative health.”

Dr. Ernst begins by reviewing the relationship between “alternative” health and evidence based medicine:

I have said it so often that I hesitate to say it again: the concepts of EBM are not a threat but an unprecedented opportunity for CAM [Complementary and Alternative Medicine]. EBM does not focus on mechanisms of action or basic sciences … It merely asks, ‘does it work?’ This open-minded approach is therefore uniquely suited for testing the value of CAM …


What I have seen happening recently is almost the opposite. If the results do not fit the preconceived ideas of CAM proponents, the findings tend to be dismissed. In such instances CAM enthusiasts tend to declare the studies in question to be fatally flawed. If trial after trial is negative, the old argument re-emerges … Scientific rationality, they argue, is for testing washing machines and guns but ‘for understanding what passes between humans… [it] is not adequate’…

In other words, there is a double standard:

Rigorous proof, it seems, is the standard for conventional health care, and study designs that cannot possibly generate a negative result are being promoted as the standard that CAM enthusiasts would like to see applied to CAM. Observational data might then masquerade as proof of effectiveness, while unbiased studies are deemed to be not applicable to CAM.

… Scientific testing of CAM is acceptable, perhaps even desirable … but the results have to be positive. If they are not, then the level of scientific rigor is swiftly lowered until finally – BINGO – a (false)-positive result is being generated. Science has thus become a tool not for testing (its true purpose) but for proving that one’s preconceived ideas were correct.

That double standard is integral to science denialism.

Rigorous proof is the benchmark in science. It is not the benchmark in denialism. Scientific research is desirable, but the results have to confirm denialism. If they don’t, the level of scientific rigor is swiftly lowered until finally the desired (but false) result is achieved. Denialists use science only when it supports their pre-determined conclusions.

That’s a double standard.