The great artist Francis Bacon summed up the human condition of confirmation bias when he said: “The mind of man is far from the nature of a clear and equal glass, wherein the beams of things should reflect according to their true incidence; nay, it is rather like an enchanted glass, full of superstition and imposture.”

A whiff of history

My dog can smell time. Her understanding of scents is so fine-tuned that she can determine how long it has been since a smell was laid down. Every scent tells her something about what happened earlier. Imagine walking out of your home and being able to see who had been by, and how long ago. An equivalent for us would be if we could see gradually fading traces of people and strollers and cars and bikes and where they had been and gone.

The ability to smell recent history is something we don’t have. We’re oblivious to it. And dogs can hear sounds that we have no idea are even being generated. We are deaf to them. And while my dog is pretty amazing, she can also be blinded by her own biases and assumptions.

There is a grey cat on our street that bullies all the other cats, and she torments all the dogs. She even bothers the elderly lady who lives in the house next to her. This cat is a piece of work.

The cat sometimes sits under a car in the driveway next door to our house. And, once in a blue moon, when I take my dog out for a walk, the cat will be there sitting under the car glowering at everything that passes. That’s when my dog tries to rip my arm out of its socket while she lunges for the cat, who simply yawns and looks bored because she knows my dog is far too big to get under the car.

After the dog saw the cat under the car a few times, she took to coming out of the house and wanting to look underneath the car before proceeding down the street. Ninety-nine percent of the time the cat is not there. But my dog looks anyways.

Occasionally I’ll spot the cat across the street. But my dog, so intent on checking under the car, will be oblivious to the cat. And I, of course, will be blissfully unaware of the history of who has just walked past, and I’ll miss everything happening in the frequencies I can’t hear. We all have our blind spots.

I knew it was confirmation bias

We are hard-wired to have cognitive biases. It’s the way our brains function. Cognitive biases help us make quick decisions about almost everything we do. Chief among them is confirmation bias: “the tendency to search for, interpret, favour, and recall information in a way that affirms one’s prior beliefs or hypotheses.”

Confirmation bias is not newly discovered. It was what Julius Caesar was talking about when he said, “Men in general are quick to believe that which they wish to be true,” and what Voltaire was speaking about when he quipped that “The human brain is a complex organ with the wonderful power of enabling man to find reasons for continuing to believe whatever it is that he wants to believe.”

It’s a bias that can have deadly effects.

Heal me, please

We count on physicians to save lives. But when cognitive biases get in the way, people can die. Consider a case recounted in by Dr. Pat Croskerry in this report on cognitive bias in clinical decision making.

An 18-year-old woman is referred by her family doctor to psychiatry for symptoms of severe anxiety and depression. She has been experiencing frequent episodes of shortness of breath, cramps in her hands and feet, and loss of consciousness. The admitting psychiatrist wants to rule out a respiratory problem, so he sends her to the emergency department for an X-ray to check for pneumonia.

The patient is obese, has asthma, and smokes. Her complaint is that she is breathless; otherwise, she is not in distress. Her chest exam is normal. So is the blood work and chest X-ray. The doctor “believes the patient can be safely returned to the psychiatric facility. He attributes her respiratory problems to anxiety.”

“While she awaits transfer, she becomes very agitated and short of breath. Several nurses attempt to settle her, encouraging her to breathe into a paper bag” (which is standard treatment for people hyperventilating due to panic or anxiety). Shortly afterward she loses consciousness and, despite heroic efforts, dies.

“The autopsy shows she had an infected blood clot in her pelvis that cut off her blood flow and therefore her ability to breathe normally. She had multiple older clots, indicating this was not the first time she had suffered such a blockage.

“Several cognitive failures probably influence the outcome in this case,” Dr. Croskerry writes. “The patient’s diagnosis of anxiety established ‘momentum’…and although she may have had hyperventilation due to anxiety, other possibilities were not ruled out earlier on in her care.”

The focus on her anxiety led physicians to ignore other possible causes for her breathing problems.

Confirmation bias can kill. But it can also leave you rotting in jail.

You got the wrong guy

Criminal justice is another area where cognitive biases can have profoundly negative effects. In a study of 50 cases of wrongful convictions, criminology professors Kim Rossmo and Joycelyn Pollock found confirmation bias was a driving factor in three-quarters of the cases, while “tunnel vision” was implicated in half. These cognitive failures were also linked to other problems, like “a rush to judgement” and “improper interrogations.”

The results can be tragic.

One of the cases analysed by Rossmo and Pollock is that of Bruce Lisker. Lisker was just 17 and high on methamphetamines when he came home and discovered his mother stabbed to death. He immediately called 911. When medics arrived, his hands were covered with blood.

“The first detective on the scene knew Bruce from prior interactions and considered him a ‘punk.’ Investigators coerced a confession (quickly recanted) from the 17-year-old teenager through the offer of a plea bargain,” Rossmo and Pollock reported.

“A rush to judgment followed by tunnel vision led to confirmation bias. Exculpatory evidence was ignored, while the alibi of an alternative and viable suspect was never checked despite inconsistencies in his story.”

Bruce rotted in jail for 26 years before it was determined that he was innocent and that someone else had killed his mother. At age 43, he emerged from prison all too aware of the impact cognitive biases can have on how we view information and make judgements.

Confirmation bias and insights

It is relatively easy to spot confirmation bias in others. Ever been to a focus group where the product manager spends most of the session complaining that these respondents “are not the right people” when they say things that run contrary to her expectations? Or seizes on the one thing that confirms her assumptions while ignoring the rest of what was said? It happens all the time.

The same thing happens with insight professionals. It’s just harder to detect in ourselves. It’s very easy to gravitate toward information that “makes sense” and gloss over or outright ignore data that doesn’t fit with our current view of the market.

We’ll leave the last word on confirmation bias to comedian Jon Ronson: “Ever since I first learned about confirmation bias, I’ve been seeing it everywhere.”

Andrew Grenville is Chief Research Officer at Maru/Matchbox.