Confirmation Bias

Jan 29, 2010

“The kids are crazy today it must be a full moon.”    This and other similar notions are widely held.  For example, people working in Emergency Departments (ED) assume that spikes in ED admissions are linked to the phase of the moon.  Again, the thinking is that the full moon brings out the craziness in people’s behavior.  Similar links are firmly held about the relationship between the consumption of sugar and bad behavior in children.  They believe that when children eat sugar, it is like consuming an amphetamine – they get wild!


Such cause and effect notions are easily dismissed when you look closely at the laws of physics or the biological plausibility of the effects of sugar on behavior.  Further, if you actually look at the numbers of ED Admissions or behavior problems in schools and the phases of the moon or sugar consumption, there are no relationships. PERIOD! End of story!  Yet, these beliefs are firmly held despite the evidence; which is not necessarily widely available.  Why is it that we hold onto such notions?


The answer is Confirmation Bias.  We are inclined to take in, and accept as true, information that supports our belief systems and miss, ignore, or discount information that runs contrary to our beliefs.  For example, a full moon provides a significant visual reference to which memories can be linked.  And because there is a widely held mythical belief that full moons affect behavior, we also remember those confirmations more clearly.  We are less likely to remember similarly bad days that lack such a strikingly visual reference point and that do not support our beliefs.  As a result, we are less likely to use that data to challenge the myth.


This bias is not limited to full moons and sugar.  It transcends rational thought and is pervasive throughout the human race.  It shapes our religious and political beliefs, our parenting choices, our teaching strategies, and our romantic and social relationships.  It also plays a significant role in the development of stereotypes and the maintenance of prejudices.  These beliefs, good or bad, when challenged, tend to elicit emotional responses (this is a topic all its own).  Much has been written about these phenomena, pertaining to issues related to how and why this occurs.  There are other factors as well that play a role in this erroneous thought process (e.g., communal reinforcement, folklore, the media, attribution error, expectancy effect, and Spinoza’s Conjecture); however, my goal is to raise your awareness of this bias, because knowing that we are prone to it may help us avoid drawing mistaken conclusions. Bottom line – it may help us open and widen our minds to different ideas and maybe even challenge some long held mistaken beliefs.


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7 Responses so far | Have Your Say!

  1. Moral Instinct - How Do You Think?
    February 19th, 2010 at 8:47 am #

    […] compound theses moralistically different vantage points with other common errors of thought (e.g., confirmation bias, fundamental attribution error), and a lack of rules of engagement, it is no wonder that our (US) […]

  2. Do we all get a fair start? « How Do You Think?
    October 16th, 2010 at 6:21 pm #

    […] that many of us hold about the poor is inaccurate and maintained both by attribution error and confirmation bias.  And the belief that many white middle class college-educated people hold – that they alone are […]

  3. Narrative Fallacy » How Do You Think? - A personal exploration of science, skepticism, and how we think.
    March 13th, 2011 at 5:40 pm #

    […] easy to see how powerful this inclination is.  Look at the prevalence of beliefs about things like full moons and bad behavior.  And how about bad behavior and acts of nature?  Pat Robertson blamed Katrina […]

  4. The Brain’s False Idols - How Do You Think?
    September 26th, 2012 at 12:06 pm #

    […] first idol can be summed up as the universal transcendent human tendencies toward Pareidolia, Confirmation Bias, and Spinoza’s Conjecture.  In other words, humans instinctively: (a) make patterns out of […]

  5. The Illusion of Cause – Vaccines and Autism - How Do You Think?
    September 26th, 2012 at 8:41 pm #

    […] prone to perceive patterns that are consistent with or confirm that belief. We are all prone to Confirmation Bias – an inclination to take in, and accept as true, information that supports our belief systems […]

  6. Cheaters - How Do You Think?
    March 28th, 2013 at 8:22 am #

    […] fit within our expectations.  These tendencies are explained by our inclinations toward confirmation bias and inattentional blindness.   Finally, there is the fundamental attribution error which leads us […]

  7. December 10 2017 – The Moral Instinct – Gatwick City Times
    December 4th, 2017 at 7:50 pm #

    […] compound these moralistically different vantage points with other common errors of thought (e.g., confirmation bias, fundamental attribution error), and a lack of rules of engagement, it is no wonder that our (US) […]

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