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Knowledge Vs. Certainty In Medicine

“I don’t want knowledge. I want certainty!” — David Bowie, from Law (Earthlings on Fire)

If there’s a trait among humans that seems universal, it appears to be an unquenchable thirst for certainty. It is likely to be a major force that drives people into the arms of religion, even radical religions that have clearly irrational views, such as the idea that flying planes into large buildings and killing thousands of people is a one-way ticket to heaven.

However, this craving for certainty isn’t expressed only by religiosity. As anyone who accepts science as the basis of medical therapy knows, there’s a lot of the same psychology going on in medicine as well. This should come as no surprise to those committed to science-based medicine because there is a profound conflict between our human desire for certainty and the uncertainty that is always inherent in so much of our medical knowledge. The reason is that the conclusions of science are always provisional, and those of science-based medicine arguably even more so than many other branches of science.

In fact, one of the hardest things for many people to accept about science-based medicine is that the conclusions of science are always subject to change based on new evidence, sometimes so much so that even those of us “in the biz” can become a bit disconcerted at the rate at which knowledge we had thought to be secure changes.

For example, think of how duodenal peptic ulcer disease was treated 25 years ago and then think about how it is treated now. Between 1984 and 1994, a revolution occurred on the basis of the discovery of H. pylori as the cause of most of the gastric and peptic ulcer disease we see. Where in 1985 we treated PUD with H2-blockers and other drugs designed to block gastric acid secretion, now antibiotics represent the mainstay of treatment and are curative at a much higher success rate than any treatment other than surgery and without the complications of surgery.

I’m sure any other physician here could come up with multiple other examples. In my own field of breast cancer surgery, I look back at how we treated breast cancer 22 years ago, when I first started residency, and how we treat it now, and I marvel at the changes. If such changes can be disconcerting even to physicians dedicated to science-based medicine, imagine how much more disconcerting they are to lay people, particularly when they hear news reports of one study that produces one result, followed just months later by a report of a different study that gives a completely different result.

We see this phenomenon of craving certainty writ large and in bold letters in huge swaths of so-called “alternative” medicine. Indeed, a lot of quackery, if not most of it, involves substituting the certainty of belief for the provisional nature of science in science-based medicine, as well as the uncertainty in our ability to predict treatment outcomes, particularly in serious diseases with variable biology, like several types of cancer.

Examples abound. Perhaps my favorite two examples include Hulda Clark, who attributed all cancer and serious disease to a common liver fluke, and Robert O. Young, who believes that virtually all disease is due to “excess acid.” So prevalent is this tendency that Harriet Hall once skewered it in a delightful post entitled The One True Cause of All Disease, where she listed a rather large samplings of things that various quacks have implicated as “the one true cause” of various diseases — or all diseases.

Time and time again, if you look carefully at “alt-med” concepts and the therapies that derive from those concepts, you find utter simplicity (or, more appropriately in many cases, simple-mindedness) tarted up with complicated-sounding jargon. Homeopathy, for instance, is at its heart nothing more than sympathetic magic, with its concept of “like cures like,” combined with the principle of contagion, with its concept that water somehow has a “memory” of the therapeutic substances with which it’s come in contact but, as Tim Minchin so hilariously put it, “it somehow forgets all the poo it’s had in it.” Reiki and other “energy healing” modalities can be summed up as “wishing makes it so,” with “intent” having the power to manipulate some fantastical life energy to heal people. It’s faith healing, pure and simple.

The simplicity of these concepts at their core makes them stubbornly resistant to evidence. Indeed, when scientific evidence meets a strong belief, the evidence usually loses. In some cases, it does more than just lose; the scientific evidence only hardens the position of believers. We see this very commonly in the anti-vaccine movement, where the more evidence is presented against a vaccine-autism link, seemingly the more deeply anti-vaccine activists dig their heels in to resist, cherry picking and twisting evidence, launching ad hominem attacks on their foes, and moving the goalposts faster than science can kick the evidence ball through the uprights. The same is true for any number of pseudoscientific beliefs. We see it all the time in quackery, where even failure of the tumor to shrink in response can lead patients to conclude that the tumor, although still there, still can’t hurt them. 9/11 Truthers, creationists, Holocaust deniers, moon hoaxers — they all engage in the same sort of desperate resistance to science.

Even those who in general accept science-based medicine can be prone to the same tendency to dismiss evidence that conflicts with their beliefs. A while back, I saw an article by Christie Aschwanden discussing just this problem. The article was entitled Convincing the Public to Accept New Medical Guidelines, and I feel it could almost have been written by Mark Crislip or myself, only minus Mark’s inimitable self-deprecating yet cutting sarcasm, or my own alleged talent for nastiness and ad hominem. (I guess I need to become more cuddly.) To set up its point that persuading people to accept the results of new medical science is exceedingly difficult, the article starts with the example of long distance runners who believe that taking ibuprofen (or “vitamin I”) before a long run reduces their pain and inflammation resulting from the run:

They call it “vitamin I.” Among runners of ultra-long-distance races, ibuprofen use is so common that when scientist David Nieman tried to study the drug’s use at the Western States Endurance Run in California’s Sierra Nevada mountains he could hardly find participants willing to run the grueling 100-mile race without it.

Nieman, director of the Human Performance Lab at Appalachian State University, eventually did recruit the subjects he needed for the study, comparing pain and inflammation in runners who took ibuprofen during the race with those who didn’t, and the results were unequivocal. Ibuprofen failed to reduce muscle pain or soreness, and blood tests revealed that ibuprofen takers actually experienced greater levels of inflammation than those who eschewed the drug. “There is absolutely no reason for runners to be using ibuprofen,” Nieman says.

The following year, Nieman returned to the Western States race and presented his findings to runners. Afterward, he asked whether his study results would change their habits. The answer was a resounding no. “They really, really think it’s helping,” Nieman says. “Even in the face of data showing that it doesn’t help, they still use it.”

As is pointed out, this is no anomaly. Aschwanden uses as another example a topic that’s become a favorite of mine over the last six months or so since the USPSTF released revised guidelines for mammographic screening. Take a look at what she says about the reaction:

This recommendation, along with the call for mammograms in women age 50 and older to be done every two years, rather than annually, seemed like a radical change to many observers. Oncologist Marisa C. Weiss, founder of, called the guidelines “a huge step backwards.” If the new guidelines are adopted, “Countless American women may die needlessly from breast cancer,” the American College of Radiology said.

“We got letters saying we have blood on our hands,” says Barbara Brenner, a breast cancer survivor and executive director of the San Francisco advocacy group Breast Cancer Action, which joined several other advocacy groups in backing the new recommendations. Brenner says the new guidelines strike a reasonable balance between mammography’s risks and benefits.

I discussed the guidelines in considerable detail twice. Let’s put it this way: I’m in the business, so to speak, and even I was shocked at the vehement reactions, not just from patients and patient advocacy groups, whose reaction I could completely understand (after many years of hearing that beginning mammography at age 40 was critical to save lives), but even from some of my very own colleagues. I was particularly disgusted by the reaction of the American College of Radiology, which was nothing more than blatant fear mongering that intentionally frightened women into thinking that the new guidelines would lead to their deaths from breast cancer. As much as we’d like to pretend otherwise, even science-based medical practitioners can fall prey to craving the certainty of known and accepted guidelines over the uncertainty of the new. And if it’s so hard to get physicians to accept new guidelines and new science, imagine how hard it is to get patients to accept them.

There is abundant evidence of how humans defend their views against evidence that would contradict them, and it’s not just observational evidence that you or I see every day. Scientists often fall prey to what University of California, Berkeley, social psychologist Robert J. MacCoun calls the “truth wins” assumption. This assumption, stated simply, is that when the truth is correctly stated it will be universally recognized. Those of us who make it one of our major activities to combat pseudoscience know, of course, that the truth doesn’t always win. Quite the contrary, actually, I’m not even sure the “truth” wins a majority of the time — or even close to a majority of the time. Moreover, most recommendations of science-based medicine are not “truth” per se; they are simply the best recommendations physicians can currently make based on current scientific evidence. Be that as it may, the problem with the “truth wins” viewpoint is that the “truth” often runs into a buzz saw known as a phenomenon that philosophers call naive realism. This phenomenon, boiled down to its essence is the belief that whatever one believes, one believes it simply because it’s true. In the service of naive realism, we all construct mental models that help us make sense of the world. When the “truth wins” assumption meets naive realism, guess what usually wins? It ain’t the truth.

At the risk of misusing the word, I’ll just point out something about our “truth”: that we all filter everything we learn through the structure of our own beliefs and the mental models we construct to support those beliefs. I like to think of science as a powerful means of penetrating the structure of those mental models, but that’s probably not a good analogy. That’s because, for science to work at changing our preconceptions, we have to have the validity of science already strongly incorporated into the structure of our own mental models. If it’s not, then science is more likely to bounce harmlessly off of the force field our beliefs create to repel it. (Sorry, I couldn’t help it; I’m a hopeless geek.) As a result, all other things being equal, when people see studies that confirm their beliefs they tend to view them as unbiased and well-designed, while if a study’s conclusions contradict a person’s beliefs that person is likely to see the study as biased and/or poorly done. As MacCoun puts it, “If a researcher produces a finding that confirms what I already believe, then of course it’s correct. Conversely, when we encounter a finding we don’t like, we have a need to explain it away.”

There’s also another strategy that people use to dismiss science that doesn’t conform to their beliefs. I hadn’t thought of this one before, but it seems obvious in retrospect after I encountered a recent study that suggested it. That mechanism is to start to lose faith in science itself as a means of making sense of nature and the world. The study was by Geoffrey D. Munro of Towson University in Maryland and appeared in the Journal of Applied Social Psychology under the title of The Scientific Impotence Excuse: Discounting Belief-Threatening Scientific Abstracts.

There were two main hypotheses and two studies included within this overall study. Basically, the hypothesis was that encountering evidence that conflicts with one’s beliefs system would tend to make the subject move toward a belief that science can’t study the hypothesis under consideration, a hypothesis known as the “scientific impotence” hypothesis or method. In essence, science is dismissed as “impotent” to study the issue where belief conflicts with evidence, thus allowing a person to dismiss the science that would tend to refute a strongly held belief. The problem, of course, is that the major side effect of asserting scientific impotence discounting is that it leads a person to distrust all science in general, or at least far more science than the science opposing that person’s belief.

Munro makes the implication of scientific impotence discounting plain:

The scientific impotence method of discounting scientific research that disconfirms a belief is certainly worrisome to scientists who tout the importance of objectivity. Even more worrisome, however, is the possibility that scientific impotence discounting might generalize beyond a specific topic to which a person has strong beliefs. In other words, once a person engages in the scientific impotence discounting process, does this erode the belief that scientific methods can answer any question? From the standpoint of the theory of cognitive dissonance (Festinger, 1957), the answer to this question could very well be “Yes.”

Not surprising, the scientific impotence discounting strategy of denying science permits one to dodge the charge of hypocrisy:

Using the scientific impotence excuse for one and only one topic as a result of exposure to belief-disconfirming information about that topic might put the individual at risk for having to acknowledge that the system of beliefs is somewhat biased and possibly hypocritical. Thus, to avoid this negative self-view, the person might arrive at the more consistent — and seemingly less biased — argument that science is impotent to address a variety of topics, one of which happens to be the topic in question.

To test these hypotheses, basically Munro had a group of students recruited for his study read various abstracts (created by investigators) that confirmed or challenged their beliefs regarding homosexuality and whether homosexuality predisposes to mental illness. It turned out that those who read belief-challenging abstracts were more prone to use scientific impotence discounting as an excuse to reject the science, while those who read belief-confirming abstracts were less likely to subscribe to the scientific impotence excuse. Controls that substituted other terms for “homosexual” demonstrated that it was the belief-disconfirming nature of the abstracts that was associated with use of scientific impotence discounting as a reason to reject the conclusions of the abstract. A second study followed up and examined more subjects. The methodology was the same as the first study, except that there were additional measures performed to see if exposure to belief-disconfirming abstracts was associated with generalization of belief in scientific impotence.

In essence, Munro found that, relative to those reading belief-confirming abstracts, participants reading belief-disconfirming abstracts indicated more belief that the topic they were reading about could not be studied scientifically and more belief that a series of other unrelated topics also could not be studied scientifically. In other words, scientific impotence discounting appears to represent a generalization of discounting of science from just science that challenges a person’s beliefs to more areas of science, if not all science. Munro concluded that being presented with belief-disconfirming scientific evidence may lead to an erosion of belief in the efficacy of scientific methods, also noting:

A number of scientific issues (e.g., global warming, evolution, stem-cell research) have extended beyond the scientific laboratories and academic journals and into the cultural consciousness. Because of their divisive and politicized nature, scientific conclusions that might inform these issues are often met with resistance by partisans on one side or the other. That is, when one has strong beliefs about such topics, scientific conclusions that are inconsistent with the beliefs may have no impact in altering those beliefs. In fact, scientific conclusions that are inconsistent with strong beliefs may even reduce one’s confidence in the scientific process more generally. Thus, in addition to the ongoing focus on creating and improving techniques that would improve understanding of the scientific process among schoolchildren, college students, and the general population, some attention should also be given to understanding how misconceptions about science are the result of belief-resistance processes and developing techniques that might short-circuit these processes.

On a strictly anecdotal level, I’ve seen this time and time again in the alt-med movement. A particularly good example is homeopathy. How many times have we seen homeopaths, when confronted with scientific evidence finding that their magic water is no more effective at anything than a placebo, claiming that their magic cannot be evaluated by randomized, double-blind clinical trials (RCTs)? The excuses are legion: RCTs are too regimented; they don’t take into account the “individualization” of homeopathic treatment; unblinded “pragmatic” trials are better; or the homeopaths’ anecdotal evidence trumps RCT evidence. Believers in alt-med then often generalize this scientific impotence discounting to many other areas of woo, claiming, for example, that science can’t adequately measure that magical mystical life energy field known as qi or even, most incredibly, that subjecting their woo to science will guarantee it to fail because belief is required and skepticism results in “negative energy.” Another common strategy I’ve seen for scientific impotence discounting is to dismiss science as “just another religion,” just as valid as whatever woo science is refuting, or to label science as “just another belief system,” as valid as any other. In other words, postmodernism!

Sadly, though, even physicians ostensibly dedicated to science-based medicine all too easily fall prey to this fallacy, although they usually don’t dismiss science as being inadequate or unable to study the question in question. Rather, they wield their preexisting belief systems and mental frameworks like a talisman to protect them from having to let disconfirming data force them to change their beliefs. Alternatively, they dismiss science itself as “just another belief.” Perhaps the most egregious example I’ve seen of this in a long time occurred, not surprisingly, over the mammogram debate from six months ago, when Dr. John Lewin, a breast imaging specialist from Diversified Radiology of Colorado and medical director of the Rose Breast Center in Denver, so infamously said, “Just the way there are Democrats and Republicans, there are people who are against mammography. They aren’t evil people. They really believe that mammography is not important.”

Wow! A straw man argument (that those who support the USPSTF guidelines are “against mammography”) combined with likening science to just another political viewpoint, and a condescending disclaimer that those who disagree with him “aren’t evil”! Mike Adams couldn’t have said it better. I wonder if Dr. Lewin thinks that Dr. Susan Love is “against mammography,” given that in the very same article it was pointed out that Dr. Love supports the USPSTF guidelines.

I get it. I really do. I get how hard it is to change one’s views. I even understand the tendency to dismiss disconfirming evidence. What I like to think distinguishes me from pseudoscientists is that I do change my mind on scientific issues as the evidence merits. Perhaps the best example of this is the aforementioned USPSTF mammography screening kerfuffle. For the longest time, I agreed enthusiastically with the prevailing medical opinion that screening for breast cancer with mammography beginning at age 40 was almost completely a universal good. Then, over the last two or three years, I’ve become increasingly aware of the problem of lead time and length bias, the Will Rogers effect, and overdiagnosis. This has led me to adjust my views about screening mammography. I haven’t adjusted them all the way to the USPSTF recommendations, but I am much more open to changes in the guidelines published late last year, even to the point that encountering the resistance of my colleagues led me to feel as though I were an anomaly.

Skepticism and science are hard in that they tend to go against some of the most deeply ingrained human traits there are, in particular the need for certainty and an intolerance of ambiguity. Also in play is our tendency to cling to our beliefs, no matter what, as though having to change our beliefs somehow devalues or dishonors us. Skepticism, critical thinking, and science can help us overcome these tendencies, but it’s difficult. Perhaps that’s the most important contribution of the scientific method. It creates a structure that allows us to change our beliefs about the world based on evidence and experimentation without the absolute necessity of taking being proven wrong personally.

When the scientific method is really embedded in the culture of scientists, it leads to the sorts of behavior described by Richard Dawkins where a scientist gives a talk with very solid evidence supporting his conclusions. That evidence, it just so happened, completely disconfirmed the long-held hypothesis championed by a very senior and respected member of his department. When the talk was over, everyone waited to see what this senior scientist would say. Instead of challenging the speaker, the scientist got up and thanked him for having shown him that he had been wrong for these many years because a phenomenon he was interested in was now better understood. True, the story may have been apocryphal or exaggerated, but that is the ideal of science. It is an ideal that is very hard, even for scientists, to live up to, and it’s even harder for non-scientists even to understand.

In the end, though, we need to strive to live up to the immortal words of Tim Minchin when describing how he’d change his mind about even homeopathy if presented with adequate evidence. Actually, as much as I love Tim Minchin’s humorous take on dealing with a woman espousing a panoply of woo that would rival’s collection, I’m forced to realize that Minchin is a bit too flippant about the difficulty in changing one’s mind. I know, I know, he’s a comic musician (or a musical comedian); flippancy is part of his job. Even so, show me, for example, strong evidence that vaccines are associated with autistic regression, and I might not “spin on a dime” and change my beliefs, as Minchin put it, but eventually, if the evidence is of a quality and quantity to cast serious doubt on the existing scientific evidence that does not support a vaccine-autism link, I will adjust my views to fit the evidence and science. I’m also under no illusion about how difficult that would be to do or that I might even be prone to using some of the defense mechanisms described by psychologists to avoid doing that, at least at first. But I’ve changed my mind before based on science disconfirming medical dogma that I had long believed on more than one occasion. I can (and no doubt will) do it again.

In the end, I want knowledge, both to provide the best care possible for my patients and just for knowledge’s sake. Science is the best way to get that knowledge about the natural world, and no other methodology has improved the treatment of human disease as fast as science-based medicine. The price is one that I’m willing to pay: Uncertainty and the expectation that much of what I “know” now will one day have to change. What they told me my first day in medical school really is true. Twenty years after I graduated, at least half of what I was taught in medical school has changed or is no longer applicable to patient care, and that’s a good thing.

Certainty is nice, but I’ve learned to live without it.

REFERENCE: Munro, G. (2010). The Scientific Impotence Excuse: Discounting Belief-Threatening Scientific Abstracts Journal of Applied Social Psychology, 40 (3), 579-600 DOI: 10.1111/j.1559-1816.2010.00588.x

*This blog post was originally published at Science-Based Medicine*

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