Editing Confirmation bias (section)

== Discovery ==
=== Informal observations ===
[[File:Somer Francis Bacon.jpg|thumb|upright|alt=Engraved head-and-shoulders portrait of Francis Bacon wearing a hat and ruff.|[[Francis Bacon]]]]
Before psychological research on confirmation bias, the phenomenon had been observed throughout history. Beginning with the Greek historian [[Thucydides]] ({{circa|460&nbsp;BC}}&nbsp;– {{circa|395&nbsp;BC}}), who wrote of misguided reason in ''[[History of the Peloponnesian War|The Peloponnesian War]]''; "...&nbsp;for it is a habit of mankind to entrust to careless hope what they long for, and to use sovereign reason to thrust aside what they do not fancy".<ref>{{Thucydides|en|4|108|4|shortref}}.</ref> Italian poet [[Dante Alighieri]] (1265–1321) noted it in the ''[[Divine Comedy]]'', in which [[St. Thomas Aquinas]] cautions Dante upon meeting in Paradise, "opinion—hasty—often can incline to the wrong side, and then affection for one's own opinion binds, confines the mind".<ref>Alighieri, Dante. ''Paradiso'' canto XIII: 118–120. Trans. Allen Mandelbaum.</ref> [[Ibn Khaldun]] noticed the same effect in his ''[[Muqaddimah]]'':<ref>{{Citation |title=The Muqadimmah |author=Ibn Khaldun |publisher=[[Princeton University Press]] |location=Princeton, NJ |year=1958 |page=71}}.</ref>
{{blockquote|Untruth naturally afflicts historical information. There are various reasons that make this unavoidable. One of them is partisanship for opinions and schools. ... if the soul is infected with partisanship for a particular opinion or sect, it accepts without a moment's hesitation the information that is agreeable to it. Prejudice and partisanship obscure the critical faculty and preclude critical investigation. The result is that falsehoods are accepted and transmitted.}} In the ''[[Novum Organum]]'', English philosopher and scientist [[Francis Bacon]] (1561–1626)<ref name="baron195">{{Harvnb|Baron|2000|pp=195–196}}.</ref> noted that biased assessment of evidence drove "all superstitions, whether in astrology, dreams, omens, divine judgments or the like".<ref name="bacon">Bacon, Francis (1620). ''Novum Organum''. reprinted in {{Citation |title=The English philosophers from Bacon to Mill |editor-first=E.&nbsp;A. |editor-last=Burtt |publisher=[[Random House]] |location=New York |year=1939 |page=36}} via {{Harvnb|Nickerson|1998|p=176}}.</ref> He wrote:<ref name="bacon"/>
{{blockquote|The human understanding when it has once adopted an opinion&nbsp;...<!--"(either as being the received opinion or as being agreeable to itself)" omitted for space--> 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[.]}}
In the second volume of his ''[[The World as Will and Representation]]'' (1844), German philosopher [[Arthur Schopenhauer]] observed that "An adopted hypothesis gives us lynx-eyes for everything that confirms it and makes us blind to everything that contradicts it."<ref>{{Citation|last=Schopenhauer |first=Arthur |title=''The World as Will and Presentation'' |volume=2 |editor1-first=David |editor1-last=Carus |editor2-first=Richard E. |editor2-last=Aquila |location=New York |publisher=[[Routledge]] |year=2011 |orig-year=1844 |page=246}}.</ref>

In his essay (1897) ''[[What Is Art?]]'', Russian novelist [[Leo Tolstoy]] wrote:<ref name=":1">Tolstoy, Leo (1896). ''What Is Art?'' ch. 14 [https://www.gutenberg.org/files/43302/43302-h/43302-h.htm p. 143] {{Webarchive|url=https://web.archive.org/web/20210817153200/https://www.gutenberg.org/files/43302/43302-h/43302-h.htm |date=17 August 2021 }}. Translated from Russian by Aylmer Maude, New York, 1904. [https://www.gutenberg.org/files/64908/64908-h/64908-h.htm Project Gutenberg edition] {{Webarchive|url=https://web.archive.org/web/20210807151038/https://www.gutenberg.org/files/64908/64908-h/64908-h.htm |date=7 August 2021 }} released 23 March 2021. Retrieved 17 August 2021.</ref>
{{blockquote|I know that most men—not only those considered clever, but even those who are very clever, and capable of understanding most difficult scientific, mathematical, or philosophic problems—can very seldom discern even the simplest and most obvious truth if it be such as to oblige them to admit the falsity of conclusions they have formed, perhaps with much difficulty—conclusions of which they are proud, which they have taught to others, and on which they have built their lives.}} In his essay (1894) ''[[The Kingdom of God Is Within You]]'', Tolstoy had earlier written:<ref name=":2">Tolstoy, Leo (1894). ''The Kingdom of God Is Within You'' [https://www.gutenberg.org/files/43302/43302-h/43302-h.htm p. 49] {{Webarchive|url=https://web.archive.org/web/20210817153200/https://www.gutenberg.org/files/43302/43302-h/43302-h.htm |date=17 August 2021 }}. Translated from Russian by Constance Garnett, New York, 1894. [https://www.gutenberg.org/files/43302/43302-h/43302-h.htm Project Gutenberg edition] {{Webarchive|url=https://web.archive.org/web/20210817153200/https://www.gutenberg.org/files/43302/43302-h/43302-h.htm |date=17 August 2021 }} released 26 July 2013. Retrieved 17 August 2021.</ref>
{{Blockquote|text=The most difficult subjects can be explained to the most slow-witted man if he has not formed any idea of them already; but the simplest thing cannot be made clear to the most intelligent man if he is firmly persuaded that he knows already, without a shadow of doubt, what is laid before him.|author=|title=|source=}}

=== Hypothesis-testing (falsification) explanation (Wason) ===
{{Main|Wason selection task}}

In Peter Wason's initial experiment published in 1960 (which does not mention the term "confirmation bias"), he repeatedly challenged participants to identify a rule applying to triples of numbers. They were told that (2,4,6) fits the rule. They generated triples, and the experimenter told them whether each triple conformed to the rule.<ref name="nickerson"/>{{rp|179}}

The actual rule was simply "any ascending sequence", but participants had great difficulty in finding it, often announcing rules that were far more specific, such as "the middle number is the average of the first and last".<ref>{{Harvnb|Wason|1960}}</ref> The participants seemed to test only positive examples—triples that obeyed their hypothesized rule. For example, if they thought the rule was, "Each number is two greater than its predecessor," they would offer a triple that fitted (confirmed) this rule, such as (11,13,15) rather than a triple that violated (falsified) it, such as (11,12,19).<ref>{{Harvnb|Lewicka|1998|page=238}}</ref>

Wason interpreted his results as showing a preference for confirmation over falsification, hence he coined the term "confirmation bias".{{Efn|Wason also used the term "verification bias".{{Sfn|Poletiek|2001|p=73}}}}<ref name="oswald">{{Harvnb|Oswald|Grosjean|2004|pp=79–96}}</ref> Wason also used confirmation bias to explain the results of his [[Wason selection task|selection task]] experiment.<ref>{{Citation |last=Wason |first=Peter C. |year=1968 |title=Reasoning about a rule |journal=Quarterly Journal of Experimental Psychology |issn= 1747-0226 |volume=20 |issue=3 |pages=273–278 |doi=10.1080/14640746808400161 |pmid=5683766|s2cid=1212273 }}</ref> Participants repeatedly performed badly on various forms of this test, in most cases ignoring information that could potentially refute (falsify) the specified rule.<ref name="sutherland" /><ref>{{Citation |last1=Barkow |first1=Jerome H. |first2=Leda |last2=Cosmides |first3=John |last3=Tooby |title=The adapted mind: evolutionary psychology and the generation of culture |publisher=[[Oxford University Press]] US |year=1995 |pages=[https://archive.org/details/adaptedmindevolu0000unse/page/181 181–184] |isbn=978-0-19-510107-2 |oclc=33832963 |url=https://archive.org/details/adaptedmindevolu0000unse/page/181 }}</ref>

=== Hypothesis testing (positive test strategy) explanation (Klayman and Ha) ===
Klayman and Ha's 1987 paper argues that the Wason experiments do not actually demonstrate a bias towards confirmation, but instead a tendency to make tests consistent with the working hypothesis.<ref name="klaymanha" /><ref>{{Harvnb|Oswald|Grosjean|2004|pp=81–82, 86–87}}</ref> They called this the "positive test strategy".<ref name=kunda112 /> This strategy is an example of a [[heuristics in judgment and decision making|heuristic]]: a reasoning shortcut that is imperfect but easy to compute.<ref name="plous233">{{Harvnb|Plous|1993|p=233}}</ref> Klayman and Ha used [[Bayesian probability]] and [[information theory]] as their standard of hypothesis-testing, rather than the falsificationism used by Wason. According to these ideas, each answer to a question yields a different amount of information, which depends on the person's prior beliefs. Thus a scientific test of a hypothesis is one that is expected to produce the most information. Since the information content depends on initial probabilities, a positive test can either be highly informative or uninformative. Klayman and Ha argued that when people think about realistic problems, they are looking for a specific answer with a small initial probability. In this case, positive tests are usually more informative than negative tests.<ref name="klaymanha">{{Citation |last1=Klayman |first1=Joshua |first2=Young-Won |last2=Ha |year=1987 |title=Confirmation, disconfirmation and information in hypothesis testing |journal=[[Psychological Review]] |volume=94 |issue=2 |pages=211–228 |issn=0033-295X |url=http://www.stats.org.uk/statistical-inference/KlaymanHa1987.pdf |access-date=14 August 2009 |doi=10.1037/0033-295X.94.2.211 |citeseerx=10.1.1.174.5232 |s2cid=10853196 |archive-date=1 October 2011 |archive-url=https://web.archive.org/web/20111001031955/http://www.stats.org.uk/statistical-inference/KlaymanHa1987.pdf |url-status=live }}</ref> However, in Wason's rule discovery task the answer—three numbers in ascending order—is very broad, so positive tests are unlikely to yield informative answers. Klayman and Ha supported their analysis by citing an experiment that used the labels "DAX" and "MED" in place of "fits the rule" and "doesn't fit the rule". This avoided implying that the aim was to find a low-probability rule. Participants had much more success with this version of the experiment.<ref>{{Harvnb|Lewicka|1998|page=239}}</ref><ref>{{Citation |last1=Tweney |first1=Ryan D. |first2=Michael E. |last2=Doherty |year=1980 |title=Strategies of rule discovery in an inference task |journal=[[The Quarterly Journal of Experimental Psychology]]|issn=1747-0226 |volume=32 |issue=1 |pages= 109–123 |doi=10.1080/00335558008248237|s2cid=143148831 }} (Experiment&nbsp;IV)</ref>

{| style="margin:auto"
|-valign="top"
| [[Image:Klayman Ha1.svg|thumb|alt=Within the universe of all possible triples, those that fit the true rule are shown schematically as a circle. The hypothesized rule is a smaller circle enclosed within it. |If the true rule (T) encompasses the current hypothesis (H), then positive tests (examining an H to see if it is T) will not show that the hypothesis is false.]]
| [[Image:Klayman Ha2.svg|thumb|alt=Two overlapping circles represent the true rule and the hypothesized rule. Any observation falling in the non-overlapping parts of the circles shows that the two rules are not exactly the same. In other words, those observations falsify the hypothesis.|If the true rule (T) ''overlaps'' the current hypothesis (H), then either a negative test or a positive test can potentially falsify H.]]
| [[Image:Klayman ha3 annotations.svg|thumb|alt=The triples fitting the hypothesis are represented as a circle within the universe of all triples. The true rule is a smaller circle within this.|When the working hypothesis (H) includes the true rule (T) then positive tests are the ''only'' way to falsify H.]]
|}

In light of this and other critiques, the focus of research moved away from confirmation versus falsification of an hypothesis, to examining whether people test hypotheses in an informative way, or an uninformative but positive way. The search for "true" confirmation bias led psychologists to look at a wider range of effects in how people process information.<ref>{{Harvnb|Oswald|Grosjean|2004|pp=86–89}}</ref>