OPINION16 June 2015

Bias in the spotlight: confirmation bias


Confirmation bias is a tendency people have to interpret evidence in ways that supports or preserves their existing beliefs.


For example, if someone believes in astrological star signs, they might read their horoscope and then look for evidence that supports that forecast, or interpret events in a way that supports their horoscope, even though events are almost certainly explained by different factors.

 There are two main ways in which confirmation bias can act:

  1. Biased selection of evidence. People search for and select evidence that supports their hypothesis – burying their heads in the sand when they come across evidence that contradicts a belief or discounting it. For example, it is not uncommon for people to only listen to political commentators that mirror their existing views. Positive evidence is given more weight, is more salient and is better remembered than contradicting evidence. 
  2. Biased interpretation of evidence. People often interpret ambiguous evidence as supporting their own pre-existing beliefs – this is how people with opposing views can draw opposite conclusions from the same evidence. In the words of business magnate Warren Buffet: “What the human being is best at doing is interpreting all new information so that their prior conclusions remain intact.” 

Confirmation bias can shed light on how some people can believe what most of us would consider to be completely implausible things. For example, if you believe the earth is flat (you wouldn’t be alone, the Flat Earth Society has a thriving community), you may then interpret evidence to the contrary very differently from someone who believes the world is round. Flat earth theorists put large emphasis on the fact that the sun appears like it is moving across the sky, to bolster their point that the sun is, in fact, moving relative to the earth which is stationary. The explanation that the earth turning away from the sun creates the illusion is disregarded or ignored.

Confirmation bias can also explain the extremes in points of view, for example about the performance of sportspeople.
Kevin Pietersen, the international cricketer observed the effects of confirmation bias among cricket fans. In his recent autobiography, he notes wisely:

“I do play defence, but then I go for the occasional reckless-seeming shot which seems to rub people up the wrong way… I do well and the people who like me say that is why they watch me. The people who hate me say, ‘yeah, just wait’. I do badly and the people who like me say, ‘he takes risks: that’s just what comes with the territory’. The people who hate me say, ‘told you so’. People formed their opinions of me a long time ago, and everything I have done since then is used to confirm that opinion.”

This is a clear example of noticing and seeking evidence that supports an existing belief, and discounting or not noticing contrary evidence. Keep this in mind the next time you are watching a match.

Crawford Hollingworth is founder of The Behavioural Architects