• Gerard Donley

Confirmation Bias



Seeing what you expect to see.


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Are you biased?


None of us want to believe we are biased in the way we exercise judgment. Each of us thinks we consider all relevant facts honestly and fairly before we reach a conclusion.


But we are all more biased than we know. One of the most pervasive biases we harbor is called Confirmation Bias.


Every day we accept, and even seek out, information that supports our pre-existing opinion more readily than we accept information tending to counter our beliefs. Notice how we tend to follow people we agree with on our Twitter feed. And have you ever met someone who watches both FOX News and MSNBC on a regular basis?


What is Confirmation Bias?

Psychology Today describes confirmation bias as “the natural human tendency to interpret new information in a way that confirms our pre-existing beliefs, to remember previous events in a way that confirms those beliefs, and to discount or discard information that challenges them.”


It's the reason we see huge numbers of people accepting as true what others recognize as fake news. When two apparently credible news sources present the day’s events with directly conflicting messages, viewers tend` to accept the version that agrees with their own viewpoint. Our minds are flooded daily with such overwhelming waves of data that we can’t conduct research on every factoid to decide if it is credible. Instead, we drift toward what is comfortable, the familiar sources who generally support our existing beliefs.


Watching the Trump Impeachment

Confirmation bias was on full display during the recent Trump impeachment trial. It was crystal clear to the Democrats, and to those who support them, that Trump had behaved so outrageously, and that his conduct so offended the Constitution, that he had to be removed from office.


Simultaneously, it was plainly obvious to the Republicans that the president acted well within his Constitutional duties in his dealings with the Ukrainian authorities. The Republicans were so convinced of the president’s innocence that they voted overwhelmingly to skip any witness testimony before reaching a verdict.


How could the two groups of intelligent public officials reach such diametrically opposed views of the same evidence? Confirmation bias. Every senator’s perception of each piece of evidence was determined by their party affiliation.

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Consequences of Confirmation Bias

The political fiasco we witnessed during the Trump impeachment is evidence enough that confirmation bias can be dangerous. The reality is that neither side of the political divide would openly consider the possible value of the opponent’s input. Mutual denunciation was all we heard.


As more people succumb to confirmation bias, our society grows more polarized. We increasingly block Twitter users we disagree with, or we unfriend people whose opinions conflict with our own. We each begin to build our own information silo. When you exist in such a silo, no one on the outside can challenge your ideas or expose you to information that conflicts with your thoughts.


Confirmation Bias in Medicine

Politics is only one arena where confirmation bias interferes with the proper functioning of our institutions. The same psychological phenomenon that leads politicians to be more accepting of information that supports their views also affects doctors and other healthcare professionals.


Wrong-site surgeries became so common in the early that hospitals enacted strict double and triple-checking protocols to prevent repeating tragic mistakes.


In November 2017, a Tennessee surgeon performed an intricate operation on a woman’s left kidney, implanting a small tube connected to a line running through the left side of her body. Unfortunately, it was the right kidney that needed the treatment. The patient won a $25 million judgment, but she needs kidney dialysis for the rest of her life.


In 2013, a Boston surgeon injected the wrong dye into a patient’s spine, causing the patient’s death. The doctor said he thought it was the correct dye because he couldn’t believe no one read the label on the vile before they handed it to him. He didn’t read it either. He expected the dye to be correct, so he didn’t check it.


Between 1990 and 2010, wrong-site surgeries gave rise to 9,744 medical malpractice settlements in the U.S., costing hospitals and insurers $1.3 billion.


Doctors also misdiagnose illnesses when their impression of a patient’s symptoms point to an initial answer. Once focused on the presumed diagnosis, a doctor may ask questions that solicit information confirming the early diagnosis. By moving prematurely in one direction, alternative diagnoses are considered less plausible.


Confirmation Bias in Criminal Investigation

The use of DNA testing has led to the release of hundreds of Americans who spent decades of their lives in prison for crimes they did not commit. How could so many innocent people be convicted in a criminal justice system that we believe to be the best in the world? Again, the answer is confirmation bias.


A new study detailed in the Northeastern University Law Review reveals how police investigators can slip into the trap of confirmation bias as they search for suspects, especially in highly publicized cases. Early in the investigation, once the police identify a chief suspect, investigators often tend to develop tunnel vision. Rather than collecting all evidence objectively, officers may focus on evidence that supports the theory consistent with their suspect’s guilt. Evidence tending to implicate another suspect, or evidence inconsistent with the guilt theory, is rationalized away or viewed as inconclusive.


Given the preference in our criminal justice system for conclusive case resolutions, police are unlikely to develop several equally plausible suspects. How could a jury convict anyone if there was always another plausible suspect instead of the named defendant?


Avoiding Confirmation Bias

Confirmation bias can creep into just about any scenario when you form an initial belief. You can reduce the likelihood of following a false perception down the wrong path by taking a few simple steps.


Expose yourself to multiple sources of information before you adopt a firm opinion. Hard as it may be if you are politically progressive, listen to FOX news, or another conservative media source. And, of course, if you’re a Hannity fan, spend some time listening to Rachel Maddow, or Chris Cuomo.


When you are moving toward a conclusion, try to find support for the opposite view. Bounce your thoughts off a friend or colleague. Get some feedback. If you repeatedly fail to find contrary data, then your original belief may be well-founded.


Doubt the spoon-fed facts.


Critical thinking is the main protection against the pitfalls of confirmation bias.



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