In my book, Snake Oil is Alive and Well, I devoted much attention to the psychological research explaining why judgments are frequently erroneous. In it, I analyzed several mechanisms for the formation of false beliefs (biases), a major one of which is the so-called “confirmation bias,” as discussed below:


This represents the tendency to seek or interpret evidence favorable to preexisting beliefs, and to ignore or reinterpret evidence that is unfavorable. In a comprehensive review of this subject, one renowned psychologist concluded that “If one were to attempt to identify a single problematic aspect of human reasoning that deserves attention above all others, the confirmation bias would have to be among the candidates for consideration.” He further stated that “it appears to be sufficiently strong and pervasive that one is led to wonder whether this bias, by itself, might account for a major fraction of the disputes, altercations, and misunderstanding that occur among individuals, groups, and nations.”

Most of us harbor preconceived judgments about almost everything, and we are often loath to surrender or change our original judgments.

Consider the recent debate over gun control. Jill is in support of gun control. She seeks out news stories and opinion pieces that reaffirm the need for limitations on gun sales and ownership. When she hears stories about shootings in the media, she interprets them in a way that supports her existing beliefs. Jack, on the other hand, is adamantly opposed to gun control. He seeks out news sources that are aligned with his position, and when he comes across news stories about shootings, he minimizes or suppresses them in a way that supports his current point of view.

Confirmation bias extends to politicians. We very rarely see them change their positions, which are usually driven by this bias. For example, over 100 members of Congress have rejected the notion of man-made climate change. Despite the new evidence, it is usually instantly rejected as it doesn’t conform to existing beliefs. More examples of this bias in politics, by both voters and politicians, are too numerous to list. I’ll simply leave it up to the reader to fill in the blanks!

Scientists and medical practitioners are also constantly plagued by confirmation bias. In the early days of medicine, this bias probably played a major role in the persistence of such irrational practices as bloodletting for management of all kinds of diseases. In contemporary times, the pervasiveness of this bias is demonstrated by the need to perform double-blind research studies, in which both the scientists and recipients involved are shielded from the biases stemming from preconceived notions about the disease or treatment in question.

So how can we, as individuals deal with this bias? Although many will never alter their positions in some areas such as politics, I can only counsel everyone to listen carefully rather than simply hear an opinion. Try to adopt an open mind. You may learn something new that will benefit you personally, but maybe even humanity in general!



In response to numerous inquiries from my readers about the books I have written, here is some information:

In my first book, Snake Oil is Alive and Well, cited above, I have attempted to provide a comprehensive analysis of the many common biases—in addition to confirmation bias. My second book, Health Tips and Myths, extends these principles to include many practical examples of healthy and unhealthy behavior and how easily one can be misled into wasting money and suffering dangers to health.

At the risk of crass commercialization, please consider purchasing one or both books, obtainable in both digital and hard copy versions. An outside review of my first book is noted below:



Comments by Harriet Hall, MD, science writer and contributing editor to Skeptic and Skeptical Inquirer publications and of website, Science Based Medicine:

Dr. Tavel has done an outstanding job of assembling a wealth of information. The book might have been titled “How to Think” as it teaches the reader to apply critical thinking skills to issues in medicine as well as to other areas like politics, where errors in thinking could have serious consequences. Along with covering blatant snake oil hoaxes and questionable claims from antioxidants to chelation, he delves into evidence-based medicine and shares his own conclusions based on the published data about everything from vitamins to diet. There are other books on alternative medicine, medical fraud, medical science, the pharmaceutical industry, the history of medicine, health advice, and critical thinking, but this book has all the essentials in one convenient package. A tour de force.

Link to Amazon:

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