Confirmation Bias

Confirmation bias is the tendency for an individual, or group, to search for or interpret information in such a way that it confirms their understanding of the situation. It is a type of cognitive bias and can be understood as an error of inductive inference leading to the confirmation of the hypothesis under study (ScienceDaily, n.d.).

The individual will generally not be aware that they are suffering from confirmation bias but will tend to give more attention and weight to information that supports their beliefs. "The most likely reason for the excessive influence of confirmatory information is that it is easier to deal with cognitively" (Gilovich, 1993).

Types of Confirmation Bias

Confirmation bias can influence out decision making in three ways (Wikipedia, 2011):

  1. Search for information - There is a tendency for individuals to search for evidence that supports their ideas and ignore those that don't. We may research only publications that support our theories for example or may ask questions in such a way that the answer is biased to our way of thinking. In the flightdeck, pilots may only examine instruments that they believe are giving them the information they expect to see.
  2. Biased interpretation - Two individuals may be presented with the same information, but each may interpret it differently and as such, confirmation bias has occurred. A banging noise on take-off may be interpreted by one pilot as a burst tyre, and by another as an engine stall.
  3. Memory recall - Even in the case of someone committing to an unbiased interpretation, the way individuals recall information from memory is different. This is known as selective recall. For instance, a pilot may believe he saw a black blur past the right hand side of the aircraft, at the same time an engine stalls as it ingests a bird. The pilot may instantly react as if the right hand engine has failed when it is possible that the left has stalled and shut down the wrong engine.


  • Lexington - 27th August 2006 - A CRJ100 took off from the wrong runway in pre-dawn darkness and failed to get airborne in sufficient time to clear trees at the end of the runway. The resulting crash led to the deaths of 49 passengers and crew. Multiple external cues were missed by the pilots that should have alerted them to the fact that they were on the wrong runway, instead, it is believed that the crew talked themselves into believing they were in the correct position. This after the comment was made about the lack of runway lights to which the first officer responded that he remembered several runway lights being unserviceable last time he had operated from the airfield (Croft, 2007).
  • Kegworth - 8th January 1989 - A Boeing 737-400 failed to make the runway and subsequently impacted terrain as a result of the incorrect engine being shutdown after a fan blade separated in the number one engine. After the first officer incorrectly identified the number two engine as suffering the failure, the crew continued to search for evidence that supported this theory. They also failed to seek further information on the true identity of the problem from the cabin crew and passengers. When full power was eventually applied to the number one engine after the shut-down of the second, further failures within the engine led to its full shut-down and the aircraft's loss of power.
1. Croft, J. (2007). Confirmation bias, cockpit chatter unravels Comair pilots at Lexington. Flight Global, July 2007.
2. Gilovich, T. (1993). How We Know What Isn't' So: The Fallibility of Human Reason in Everyday Life. New York: The Free Press, 1993.
2. Science Daily (n.d.). Confirmation Bias., n.d.
2. Wikipedia (2011). Confirmation Bias., August 2011.

Want to know more?

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A detailed look at the Kegworth Disaster
Confirmation Bias
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