Confirmation bias is a term used to describe a tendency for people to favor information that confirms their already held beliefs or expectations. Confirmation bias was recognized and written about as long ago as the time of Thucydides, who wrote, “it is a habit of mankind … to use sovereign reason to thrust aside what they do not fancy” (1).
Francis Bacon, in the Novum Organum, states, “The human understanding when it has once adopted an opinion… draws all things else to support and agree with it. And though there be a greater number and weight of instances to be found on the other side, yet these it either neglects or despises, or else by some distinction sets aside or rejects” (2).
(1) Thucydides; Crawley, Richard (trans) (431 BCE), “XIV”, “The History of the Peloponnesian War“, The Internet Classics Archive, retrieved 2010-05-27
(2 )Bacon, Francis (1620). Novum Organum. reprinted in Burtt, E.A., ed. (1939), The English philosophers from Bacon to Mill, New York: Random House, p. 36 via Nickerson 1998, p. 176