Confirmation bias
Encyclopedia
Confirmation bias is a tendency for people to favor information that confirms their preconceptions or hypotheses
regardless of whether the information is true.David Perkins
, a geneticist
, coined the term "myside bias" referring to a preference for "my" side of an issue. As a result, people gather evidence and recall information from memory selectively, and interpret it in a biased way
. The biases appear in particular for emotionally significant issues and for established beliefs. For example, in reading about gun control
, people usually prefer sources that affirm their existing attitudes. They also tend to interpret ambiguous evidence as supporting their existing position. Biased search, interpretation and/or recall have been invoked to explain attitude polarization
(when a disagreement becomes more extreme even though the different parties are exposed to the same evidence), belief perseverance (when beliefs persist after the evidence for them is shown to be false), the irrational primacy effect (a stronger weighting for data encountered early in an arbitrary series) and illusory correlation
(in which people falsely perceive an association between two events or situations).
A series of experiments in the 1960s suggested that people are biased towards confirming their existing beliefs. Later work explained these results in terms of a tendency to test ideas in a one-sided way, focusing on one possibility and ignoring alternatives. In combination with other effects, this strategy can bias the conclusions that are reached. Explanations for the observed biases include wishful thinking
and the limited human capacity to process information. Another proposal is that people show confirmation bias because they are pragmatically assessing the costs of being wrong, rather than investigating in a neutral, scientific way.
Confirmation biases contribute to overconfidence
in personal beliefs and can maintain or strengthen beliefs in the face of contrary evidence. Hence they can lead to poor decisions
, especially in organizational, scientific, military, political and social contexts.
, distinct from the behavioral confirmation effect, also called "self-fulfilling prophecy
", in which people behave so as to make their expectations come true. Some psychologists use "confirmation bias" to refer to any way in which people avoid rejecting a belief, whether in searching for evidence, interpreting it, or recalling it from memory. Others restrict the term to selective collection of evidence."Assimilation bias" is another term used for biased interpretation of evidence.
The preference for positive tests is not itself a bias, since positive tests can be highly informative. However, in conjunction with other effects, this strategy can confirm existing beliefs or assumptions, independently of whether they are true. In real-world situations, evidence is often complex and mixed. For example, various contradictory ideas about someone could each be supported by concentrating on one aspect of his or her behavior. Thus any search for evidence in favor of a hypothesis is likely to succeed. One illustration of this is the way the phrasing of a question can significantly change the answer. For example, people who are asked, "Are you happy with your social life?" report greater satisfaction than those asked, "Are you unhappy with your social life?"
Even a small change in the wording of a question can affect how people search through available information, and hence the conclusions they reach. This was shown using a fictional child custody case. Subjects read that Parent A was moderately suitable to be the guardian in multiple ways. Parent B had a mix of salient positive and negative qualities: a close relationship with the child but a job that would take him or her away for long periods. When asked, "Which parent should have custody of the child?" the subjects looked for positive attributes and a majority chose Parent B. However, when the question was, "Which parent should be denied custody of the child?" they looked for negative attributes, but again a majority answered Parent B, implying that Parent A should have custody.
Similar studies have demonstrated how people engage in biased search for information, but also that this phenomenon may be limited by a preference for genuine diagnostic tests, where they are available. In an initial experiment, subjects had to rate another person on the introversion-extroversion personality dimension on the basis of an interview. They chose the interview questions from a given list. When the interviewee was introduced as an introvert, the subjects chose questions that presumed introversion, such as, "What do you find unpleasant about noisy parties?" When the interviewee was described as extroverted, almost all the questions presumed extroversion, such as, "What would you do to liven up a dull party?" These loaded questions gave the interviewees little or no opportunity to falsify the hypothesis about them. However, a later version of the experiment gave the subjects less presumptive questions to choose from, such as, "Do you shy away from social interactions?" Subjects preferred to ask these more diagnostic questions, showing only a weak bias towards positive tests. This pattern, of a main preference for diagnostic tests and a weaker preference for positive tests, has been replicated in other studies.
Another experiment gave subjects a particularly complex rule-discovery task involving moving objects simulated by a computer. Objects on the computer screen followed specific laws, which the subjects had to figure out. They could "fire" objects across the screen to test their hypotheses. Despite making many attempts over a ten hour session, none of the subjects worked out the rules of the system. They typically sought to confirm rather than falsify their hypotheses, and were reluctant to consider alternatives. Even after seeing evidence that objectively refuted their working hypotheses, they frequently continued doing the same tests. Some of the subjects were instructed in proper hypothesis-testing, but these instructions had almost no effect.
A team at Stanford University
ran an experiment with subjects who felt strongly about capital punishment, with half in favor and half against. Each of these subjects read descriptions of two studies; a comparison of U.S. state
s with and without the death penalty, and a comparison of murder rates in a state before and after the introduction of the death penalty. After reading a quick description of each study, the subjects were asked whether their opinions had changed. They then read a much more detailed account of each study's procedure and had to rate how well-conducted and convincing that research was. In fact, the studies were fictional. Half the subjects were told that one kind of study supported the deterrent effect and the other undermined it, while for other subjects the conclusions were swapped.
The subjects, whether proponents or opponents, reported shifting their attitudes slightly in the direction of the first study they read. Once they read the more detailed descriptions of the two studies, they almost all returned to their original belief regardless of the evidence provided, pointing to details that supported their viewpoint and disregarding anything contrary. Subjects described studies supporting their pre-existing view as superior to those that contradicted it, in detailed and specific ways. Writing about a study that seemed to undermine the deterrence effect, a death penalty proponent wrote, "The research didn't cover a long enough period of time", while an opponent's comment on the same study said, "No strong evidence to contradict the researchers has been presented". The results illustrated that people set higher standards of evidence for hypotheses that go against their current expectations. This effect, known as "disconfirmation bias", has been supported by other experiments.
A study of biased interpretation took place during the 2004 US presidential election
and involved subjects who described themselves as having strong feelings about the candidates. They were shown apparently contradictory pairs of statements, either from Republican candidate George W. Bush
, Democratic candidate John Kerry
or a politically neutral public figure. They were also given further statements that made the apparent contradiction seem reasonable. From these three pieces of information, they had to decide whether or not each individual's statements were inconsistent. There were strong differences in these evaluations, with subjects much more likely to interpret statements by the candidate they opposed as contradictory.
In this experiment, the subjects made their judgments while in a magnetic resonance imaging
(MRI) scanner which monitored their brain activity. As subjects evaluated contradictory statements by their favored candidate, emotion
al centers of their brains were aroused. This did not happen with the statements by the other figures. The experimenters inferred that the different responses to the statements were not due to passive reasoning errors. Instead, the subjects were actively reducing the cognitive dissonance
induced by reading about their favored candidate's irrational or hypocritical behavior.
Biased interpretation is not restricted to emotionally significant topics. In another experiment, subjects were told a story about a theft. They had to rate the evidential importance of statements arguing either for or against a particular character being responsible. When they hypothesized that character's guilt, they rated statements supporting that hypothesis as more important than conflicting statements.
predicts that information matching prior expectations will be more easily stored and recalled. Some alternative approaches say that surprising information stands out more and so is more memorable. Predictions from both these theories have been confirmed in different experimental contexts, with no theory winning outright.
In one study, subjects read a profile of a woman which described a mix of introverted and extroverted behaviors. They later had to recall examples of her introversion and extroversion. One group was told this was to assess the woman for a job as a librarian, while a second group were told it was for a job in real estate sales. There was a significant difference between what these two groups recalled, with the "librarian" group recalling more examples of introversion and the "sales" groups recalling more extraverted behavior. A selective memory effect has also been shown in experiments that manipulate the desirability of personality types. In one of these, a group of subjects were shown evidence that extraverted people are more successful than introverts. Another group were told the opposite. In a subsequent, apparently unrelated, study, they were asked to recall events from their lives in which they had been either introverted or extraverted. Each group of subjects provided more memories connecting themselves with the more desirable personality type, and recalled those memories more quickly.
One study showed how selective memory can maintain belief in extrasensory perception (ESP). Believers and disbelievers were each shown descriptions of ESP experiments. Half of each group were told that the experimental results supported the existence of ESP, while the others were told they did not. In a subsequent test, subjects recalled the material accurately, apart from believers who had read the non-supportive evidence. This group remembered significantly less information and some of them incorrectly remembered the results as supporting ESP.
A less abstract study was the Stanford biased interpretation experiment in which subjects with strong opinions about the death penalty read about mixed experimental evidence. Twenty-three percent of the subjects reported that their views had become more extreme, and this self-reported shift correlated
strongly with their initial attitudes. In later experiments, subjects also reported their opinions becoming more extreme in response to ambiguous information. However, comparisons of their attitudes before and after the new evidence showed no significant change, suggesting that the self-reported changes might not be real. Based on these experiments, Deanna Kuhn and Joseph Lao concluded that polarization is a real phenomenon but far from inevitable, only happening in a small minority of cases. They found that it was prompted not only by considering mixed evidence, but by merely thinking about the topic.
Charles Taber and Milton Lodge argued that the Stanford team's result had been hard to replicate because the arguments used in later experiments were too abstract or confusing to evoke an emotional response. The Taber and Lodge study used the emotionally charged topics of gun control
and affirmative action
. They measured the attitudes of their subjects towards these issues before and after reading arguments on each side of the debate. Two groups of subjects showed attitude polarization; those with strong prior opinions and those who were politically knowledgeable. In part of this study, subjects chose which information sources to read, from a list prepared by the experimenters. For example they could read the National Rifle Association
's and the Brady Anti-Handgun Coalition
's arguments on gun control. Even when instructed to be even-handed, subjects were more likely to read arguments that supported their existing attitudes. This biased search for information correlated well with the polarization effect.
A typical finding is that at least some of the initial belief remains even after a full debrief. In one experiment, subjects had to distinguish between real and fake suicide notes. The feedback was random: some were told they had done well while others were told they had performed badly. Even after being fully debriefed, subjects were still influenced by the feedback. They still thought they were better or worse than average at that kind of task, depending on what they had initially been told.
In another study, subjects read job performance ratings of two firefighters, along with their responses to a risk aversion
test. These fictional data were arranged to show either a negative or positive association
between risk-taking attitudes and job success. Even if these case studies had been true, they would have been scientifically poor evidence. However, the subjects found them subjectively persuasive. When the case studies were shown to be fictional, subjects' belief in a link diminished, but around half of the original effect remained. Follow-up interviews established that the subjects had understood the debriefing and taken it seriously. Subjects seemed to trust the debriefing, but regarded the discredited information as irrelevant to their personal belief.
in which the earlier items in a series leave a stronger memory trace. Biased interpretation offers an explanation for this effect: seeing the initial evidence, people form a working hypothesis that affects how they interpret the rest of the information.
One demonstration of irrational primacy involved colored chips supposedly drawn from two urns. Subjects were told the color distributions of the urns, and had to estimate the probability of a chip being drawn from one of them. In fact, the colors appeared in a pre-arranged order. The first thirty draws favored one urn and the next thirty favored the other. The series as a whole was neutral, so rationally, the two urns were equally likely. However, after sixty draws, subjects favored the urn suggested by the initial thirty.
Another experiment involved a slide show of a single object, seen as just a blur at first and in slightly better focus with each succeeding slide. After each slide, subjects had to state their best guess of what the object was. Subjects whose early guesses were wrong persisted with those guesses, even when the picture was sufficiently in focus that other people could readily identify the object.
is the tendency to see non-existent correlations in a set of data. This tendency was first demonstrated in a series of experiments in the late 1960s. In one experiment, subjects read a set of psychiatric case studies, including responses to the Rorschach inkblot test
. They reported that the homosexual men in the set were more likely to report seeing buttocks, anuses or sexually ambiguous figures in the inkblots. In fact the case studies were fictional and, in one version of the experiment, had been constructed so that the homosexual men were less likely to report this imagery. In a survey, a group of experienced psychoanalysts reported the same set of illusory associations with homosexuality.
Another study recorded the symptoms experienced by arthritic patients, along with weather conditions over a 15-month period. Nearly all the patients reported that their pains were correlated with weather conditions, although the real correlation was zero.
This effect is a kind of biased interpretation, in that objectively neutral or unfavorable evidence is interpreted to support existing beliefs. It is also related to biases in hypothesis-testing behavior. In judging whether two events, such as illness and bad weather, are correlated, people rely heavily on the number of positive-positive cases: in this example, instances of both pain and bad weather. They pay relatively little attention to the other kinds of observation (of no pain and/or good weather). This parallels the reliance on positive tests in hypothesis testing. It may also reflect selective recall, in that people may have a sense that two events are correlated because it is easier to recall times when they happened together.
In the above fictional example, arthritic symptoms are more likely on days with no rain. However, people are likely to focus on the relatively large number of days which have both rain and symptoms. By concentrating on one cell of the table rather than all four, people can misperceive the relationship, in this case associating rain with arthritic symptoms.
(c. 460 BC – c. 395 BC), Italian poet Dante Alighieri
(1265–1321), English philosopher and scientist Francis Bacon
(1561–1626), and Russian author Leo Tolstoy
(1828–1910). Thucydides, in the History of the Peloponnesian War
wrote, "it is a habit of mankind ... to use sovereign reason to thrust aside what they do not fancy." In the Divine Comedy, St. Thomas Aquinas cautions Dante when they meet in Paradise, "opinion—hasty—often can incline to the wrong side, and then affection for one's own opinion binds, confines the mind." Bacon, in the Novum Organum
, wrote,
Bacon said that biased assessment of evidence drove "all superstitions, whether in astrology, dreams, omens, divine judgments or the like". In his essay "What Is Art?
", Tolstoy wrote,
. For an experiment published in 1960, he challenged subjects to identify a rule applying to triples of numbers. At the outset, they were told that (2,4,6) fits the rule. Subjects could generate their own triples and the experimenter told them whether or not each triple conformed to the rule.
While the actual rule was simply "any ascending sequence", the subjects had a great deal of difficulty in arriving at it, often announcing rules that were far more specific, such as "the middle number is the average of the first and last". The subjects 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 fit this rule, such as (11,13,15) rather than a triple that violates it, such as (11,12,19).
Wason accepted falsificationism, according to which a scientific test of a hypothesis is a serious attempt to falsify it. He interpreted his results as showing a preference for confirmation over falsification, hence the term "confirmation bias".Wason also used the term "verification bias". Wason also used confirmation bias to explain the results of his selection task
experiment. In this task, subjects are given partial information about a set of objects, and have to specify what further information they would need to tell whether or not a conditional rule
("If A, then B") applies. It has been found repeatedly that people perform badly on various forms of this test, in most cases ignoring information that could potentially refute the rule.
: a reasoning shortcut that is imperfect but easy to compute. 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. 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. Subjects had much more success with this version of the experiment.
In light of this and other critiques, the focus of research moved away from confirmation versus falsification to examine 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.
Cognitive explanations for confirmation bias are based on limitations in people's ability to handle complex tasks, and the shortcuts, called "heuristics", that they use. For example, people may judge the reliability of evidence by using the availability heuristic
, i.e. how readily a particular idea comes to mind. It is also possible that people can only focus on one thought at a time, so find it difficult to test alternative hypotheses in parallel. Another heuristic is the positive test strategy identified by Klayman and Ha, in which people test a hypothesis by examining cases where they expect a property or event to occur. This heuristic avoids the difficult or impossible task of working out how diagnostic each possible question will be. However, it is not universally reliable, so people can overlook challenges to their existing beliefs.
Motivational explanations involve an effect of desire
on belief
, sometimes called "wishful thinking
". It is known that people prefer pleasant thoughts over unpleasant ones in a number of ways: this is called the "Pollyanna principle
". Applied to argument
s or sources of evidence
, this could explain why desired conclusions are more likely to be believed true. According to experiments that manipulate the desirability of the conclusion, people demand a high standard of evidence for unpalatable ideas and a low standard for preferred ideas. In other words, they ask, "Can I believe this?" for some suggestions and, "Must I believe this?" for others. Although consistency
is a desirable feature of attitudes, an excessive drive for consistency is another potential source of bias because it may prevent people from neutrally evaluating new, surprising information. Social psychologist Ziva Kunda
combines the cognitive and motivational theories, arguing that motivation creates the bias, but cognitive factors determine the size of the effect.
Explanations in terms of cost-benefit analysis
assume that people do not just test hypotheses in a disinterested way, but assess the costs of different errors. Using ideas from evolutionary psychology
, James Friedrich suggests that people do not primarily aim at truth
in testing hypotheses, but try to avoid the most costly errors. For example, employers might ask one-sided questions in job interviews because they are focused on weeding out unsuitable candidates. Yaacov Trope and Akiva Liberman's refinement of this theory assumes that people compare the two different kinds of error: accepting a false hypothesis or rejecting a true hypothesis. For instance, someone who underestimates a friend's honesty might treat him or her suspiciously and so undermine the friendship. Overestimating the friend's honesty may also be costly, but less so. In this case, it would be rational to seek, evaluate or remember evidence of their honesty in a biased way. When someone gives an initial impression of being introverted or extraverted, questions that match that impression come across as more empathic. This suggests that when talking to someone who seems to be an introvert, it is a sign of better social skills
to ask, "Do you feel awkward in social situations?" rather than, "Do you like noisy parties?" The connection between confirmation bias and social skills was corroborated by a study of how college students get to know other people. Highly self-monitoring students, who are more sensitive to their environment and to social norms, asked more matching questions when interviewing a high-status staff member than when getting to know fellow students.
, investors made more profit when they resisted bias. For example, participants who interpreted a candidate's debate performance in a neutral rather than partisan way were more likely to profit. To combat the effect of confirmation bias, investors can try to adopt a contrary viewpoint "for the sake of argument". One such technique involves imagining that their investments have collapsed and asking why this might happen.
. If a patient recovered, medical authorities counted the treatment as successful, rather than looking for alternative explanations such as that the disease had run its natural course. Biased assimilation is a factor in the modern appeal of alternative medicine
, whose proponents are swayed by positive anecdotal evidence
but treat scientific evidence hyper-critically.
Cognitive therapy
was developed by Aaron T. Beck
in the early 1960s and has become a popular approach. According to Beck, biased information processing is a factor in depression
. His approach teaches people to treat evidence impartially, rather than selectively reinforcing negative outlooks. Phobias and hypochondria
have also been shown to involve confirmation bias for threatening information.
Nickerson argues that reasoning in judicial and political contexts is sometimes subconsciously biased, favoring conclusions that judges, juries or governments have already committed to. Since the evidence in a jury trial can be complex, and jurors often reach decisions about the verdict early on, it is reasonable to expect an attitude polarization effect. The prediction that jurors will become more extreme in their views as they see more evidence has been borne out in experiments with mock trial
s. Both inquisitorial
and adversarial
criminal justice systems are affected by confirmation bias.
Confirmation bias can be a factor in creating or extending conflicts, from emotionally charged debates to wars: by interpreting the evidence in their favor, each opposing party can become overconfident that it is in the stronger position. On the other hand, confirmation bias can result in people ignoring or misinterpreting the signs of an imminent or incipient conflict. For example, psychologists Stuart Sutherland
and Thomas Kida have each argued that US Admiral Husband E. Kimmel
showed confirmation bias when playing down the first signs of the Japanese attack on Pearl Harbor
.
A two-decade study of political pundits by Philip E. Tetlock
found that, on the whole, their predictions were not much better than chance. Tetlock divided experts into "foxes" who maintained multiple hypotheses, and "hedgehogs" who were more dogmatic. In general, the hedgehogs were much less accurate. Tetlock blamed their failure on confirmation bias—specifically, their inability to make use of new information that contradicted their existing theories.
"readings" is that listeners apply a confirmation bias which fits the psychic's statements to their own lives. By making a large number of ambiguous statements in each sitting, the psychic gives the client more opportunities to find a match. This is one of the techniques of cold reading
, with which a psychic can deliver a subjectively impressive reading without any prior information about the client. Investigator James Randi
compared the transcript of a reading to the client's report of what the psychic had said, and found that the client showed a strong selective recall of the "hits".
As a "striking illustration" of confirmation bias in the real world, Nickerson mentions numerological pyramidology
: the practice of finding meaning in the proportions of the Egyptian pyramids. There are many different length measurements that can be made of, for example, the Great Pyramid of Giza
and many ways to combine or manipulate them. Hence it is almost inevitable that people who look at these numbers selectively will find superficially impressive correspondences, for example with the dimensions of the Earth.
is the search for falsifying as well as confirming evidence. However, many times in the history of science
, scientists have resisted new discoveries by selectively interpreting or ignoring unfavorable data. Previous research has shown that the assessment of the quality of scientific studies seems to be particularly vulnerable to confirmation bias. It has been found several times that scientists rate studies that report findings consistent with their prior beliefs more favorably than studies reporting findings inconsistent with their previous beliefs. However, assuming that the research question is relevant, the experimental design adequate and the data are clearly and comprehensively described, the found results should be of importance to the scientific community and should not be viewed prejudicially—regardless of whether they conform to current theoretical predictions. Confirmation bias may thus be especially harmful to objective evaluations regarding nonconforming results, since biased individuals may regard opposing evidence to be weak in principle and give little serious thought to revising their beliefs. Scientific innovators often meet with resistance from the scientific community, and research presenting controversial results frequently receives harsh peer review. In the context of scientific research, confirmation biases can sustain theories or research programs in the face of inadequate or even contradictory evidence; the field of parapsychology
has been particularly affected. An experimenter's confirmation bias can potentially affect which data are reported. Data that conflict with the experimenter's expectations may be more readily discarded as unreliable, producing the so-called file drawer effect
. To combat this tendency, scientific training teaches ways to avoid bias. Experimental designs involving randomization and double blind trials, along with the social process of peer review
, are thought to mitigate the effect of individual scientists' biases, although it has been argued that such biases can play a role in the peer review process itself.
is the drive to seek positive feedback. Both are served by confirmation biases. In experiments where people are given feedback that conflicts with their self-image, they are less likely to attend to it or remember it than when given self-verifying feedback. They reduce the impact of such information by interpreting it as unreliable. Similar experiments have found a preference for positive feedback, and the people who give it, over negative feedback.
Hypothesis
A hypothesis is a proposed explanation for a phenomenon. The term derives from the Greek, ὑποτιθέναι – hypotithenai meaning "to put under" or "to suppose". For a hypothesis to be put forward as a scientific hypothesis, the scientific method requires that one can test it...
regardless of whether the information is true.David Perkins
David Perkins (geneticist)
David Dexter Perkins was an American geneticist, a member of the faculty of Stanford University for more than 58 years, from 1948 until his death in 2007. He received his PhD in Zoology in 1949 from Columbia University. A member of the National Academy of Sciences, he served as President of the...
, a geneticist
Geneticist
A geneticist is a biologist who studies genetics, the science of genes, heredity, and variation of organisms. A geneticist can be employed as a researcher or lecturer. Some geneticists perform experiments and analyze data to interpret the inheritance of skills. A geneticist is also a Consultant or...
, coined the term "myside bias" referring to a preference for "my" side of an issue. As a result, people gather evidence and recall information from memory selectively, and interpret it in a biased way
Cognitive bias
A cognitive bias is a pattern of deviation in judgment that occurs in particular situations. Implicit in the concept of a "pattern of deviation" is a standard of comparison; this may be the judgment of people outside those particular situations, or may be a set of independently verifiable...
. The biases appear in particular for emotionally significant issues and for established beliefs. For example, in reading about gun control
Gun politics
Gun politics addresses safety issues and ideologies related to firearms through criminal and noncriminal use. Gun politics deals with rules, regulations, and restrictions on the use, ownership, and distribution of firearms.-National sovereignty:...
, people usually prefer sources that affirm their existing attitudes. They also tend to interpret ambiguous evidence as supporting their existing position. Biased search, interpretation and/or recall have been invoked to explain attitude polarization
Attitude polarization
Attitude polarization, also known as belief polarization, is a phenomenon in which a disagreement becomes more extreme as the different parties consider evidence on the issue. It is one of the effects of confirmation bias: the tendency of people to search for and interpret evidence selectively, to...
(when a disagreement becomes more extreme even though the different parties are exposed to the same evidence), belief perseverance (when beliefs persist after the evidence for them is shown to be false), the irrational primacy effect (a stronger weighting for data encountered early in an arbitrary series) and illusory correlation
Illusory correlation
Illusory correlation is the phenomenon of seeing the relationship one expects in a set of data even when no such relationship exists. When people form false associations between membership in a statistical minority group and rare behaviors, this would be a common example of illusory correlation...
(in which people falsely perceive an association between two events or situations).
A series of experiments in the 1960s suggested that people are biased towards confirming their existing beliefs. Later work explained these results in terms of a tendency to test ideas in a one-sided way, focusing on one possibility and ignoring alternatives. In combination with other effects, this strategy can bias the conclusions that are reached. Explanations for the observed biases include wishful thinking
Wishful thinking
Wishful thinking is the formation of beliefs and making decisions according to what might be pleasing to imagine instead of by appealing to evidence, rationality or reality...
and the limited human capacity to process information. Another proposal is that people show confirmation bias because they are pragmatically assessing the costs of being wrong, rather than investigating in a neutral, scientific way.
Confirmation biases contribute to overconfidence
Overconfidence effect
The overconfidence effect is a well-established bias in which someone's subjective confidence in their judgments is reliably greater than their objective accuracy, especially when confidence is relatively high. For example, in some quizzes, people rate their answers as "99% certain" but are wrong...
in personal beliefs and can maintain or strengthen beliefs in the face of contrary evidence. Hence they can lead to poor decisions
Decision making
Decision making can be regarded as the mental processes resulting in the selection of a course of action among several alternative scenarios. Every decision making process produces a final choice. The output can be an action or an opinion of choice.- Overview :Human performance in decision terms...
, especially in organizational, scientific, military, political and social contexts.
Types
Confirmation biases are effects in information processingInformation processing theory
The information processing theory approach to the study of cognitive development evolved out of the American experimental tradition in psychology. Developmental psychologists who adopt the information-processing perspective account for mental development in terms of maturational changes in basic...
, distinct from the behavioral confirmation effect, also called "self-fulfilling prophecy
Self-fulfilling prophecy
A self-fulfilling prophecy is a prediction that directly or indirectly causes itself to become true, by the very terms of the prophecy itself, due to positive feedback between belief and behavior. Although examples of such prophecies can be found in literature as far back as ancient Greece and...
", in which people behave so as to make their expectations come true. Some psychologists use "confirmation bias" to refer to any way in which people avoid rejecting a belief, whether in searching for evidence, interpreting it, or recalling it from memory. Others restrict the term to selective collection of evidence."Assimilation bias" is another term used for biased interpretation of evidence.
Biased search for information
Experiments have repeatedly found that people tend to test hypotheses in a one-sided way, by searching for evidence consistent with the hypothesis they hold at a given time. Rather than searching through all the relevant evidence, they ask questions that are phrased so that an affirmative answer supports their hypothesis. They look for the consequences that they would expect if their hypothesis were true, rather than what would happen if it were false. For example, someone who is trying to identify a number using yes/no questions and suspects that the number is 3 might ask, "Is it an odd number?" People prefer this sort of question, called a "positive test", even when a negative test such as "Is it an even number?" would yield exactly the same information. However, this does not mean that people seek tests that are guaranteed to give a positive answer. In studies where subjects could select either such pseudo-tests or genuinely diagnostic ones, they favored the genuinely diagnostic.The preference for positive tests is not itself a bias, since positive tests can be highly informative. However, in conjunction with other effects, this strategy can confirm existing beliefs or assumptions, independently of whether they are true. In real-world situations, evidence is often complex and mixed. For example, various contradictory ideas about someone could each be supported by concentrating on one aspect of his or her behavior. Thus any search for evidence in favor of a hypothesis is likely to succeed. One illustration of this is the way the phrasing of a question can significantly change the answer. For example, people who are asked, "Are you happy with your social life?" report greater satisfaction than those asked, "Are you unhappy with your social life?"
Even a small change in the wording of a question can affect how people search through available information, and hence the conclusions they reach. This was shown using a fictional child custody case. Subjects read that Parent A was moderately suitable to be the guardian in multiple ways. Parent B had a mix of salient positive and negative qualities: a close relationship with the child but a job that would take him or her away for long periods. When asked, "Which parent should have custody of the child?" the subjects looked for positive attributes and a majority chose Parent B. However, when the question was, "Which parent should be denied custody of the child?" they looked for negative attributes, but again a majority answered Parent B, implying that Parent A should have custody.
Similar studies have demonstrated how people engage in biased search for information, but also that this phenomenon may be limited by a preference for genuine diagnostic tests, where they are available. In an initial experiment, subjects had to rate another person on the introversion-extroversion personality dimension on the basis of an interview. They chose the interview questions from a given list. When the interviewee was introduced as an introvert, the subjects chose questions that presumed introversion, such as, "What do you find unpleasant about noisy parties?" When the interviewee was described as extroverted, almost all the questions presumed extroversion, such as, "What would you do to liven up a dull party?" These loaded questions gave the interviewees little or no opportunity to falsify the hypothesis about them. However, a later version of the experiment gave the subjects less presumptive questions to choose from, such as, "Do you shy away from social interactions?" Subjects preferred to ask these more diagnostic questions, showing only a weak bias towards positive tests. This pattern, of a main preference for diagnostic tests and a weaker preference for positive tests, has been replicated in other studies.
Another experiment gave subjects a particularly complex rule-discovery task involving moving objects simulated by a computer. Objects on the computer screen followed specific laws, which the subjects had to figure out. They could "fire" objects across the screen to test their hypotheses. Despite making many attempts over a ten hour session, none of the subjects worked out the rules of the system. They typically sought to confirm rather than falsify their hypotheses, and were reluctant to consider alternatives. Even after seeing evidence that objectively refuted their working hypotheses, they frequently continued doing the same tests. Some of the subjects were instructed in proper hypothesis-testing, but these instructions had almost no effect.
Biased interpretation
Confirmation biases are not limited to the collection of evidence. Even if two individuals have the same information, the way they interpret it can be biased.A team at Stanford University
Stanford University
The Leland Stanford Junior University, commonly referred to as Stanford University or Stanford, is a private research university on an campus located near Palo Alto, California. It is situated in the northwestern Santa Clara Valley on the San Francisco Peninsula, approximately northwest of San...
ran an experiment with subjects who felt strongly about capital punishment, with half in favor and half against. Each of these subjects read descriptions of two studies; a comparison of U.S. state
U.S. state
A U.S. state is any one of the 50 federated states of the United States of America that share sovereignty with the federal government. Because of this shared sovereignty, an American is a citizen both of the federal entity and of his or her state of domicile. Four states use the official title of...
s with and without the death penalty, and a comparison of murder rates in a state before and after the introduction of the death penalty. After reading a quick description of each study, the subjects were asked whether their opinions had changed. They then read a much more detailed account of each study's procedure and had to rate how well-conducted and convincing that research was. In fact, the studies were fictional. Half the subjects were told that one kind of study supported the deterrent effect and the other undermined it, while for other subjects the conclusions were swapped.
The subjects, whether proponents or opponents, reported shifting their attitudes slightly in the direction of the first study they read. Once they read the more detailed descriptions of the two studies, they almost all returned to their original belief regardless of the evidence provided, pointing to details that supported their viewpoint and disregarding anything contrary. Subjects described studies supporting their pre-existing view as superior to those that contradicted it, in detailed and specific ways. Writing about a study that seemed to undermine the deterrence effect, a death penalty proponent wrote, "The research didn't cover a long enough period of time", while an opponent's comment on the same study said, "No strong evidence to contradict the researchers has been presented". The results illustrated that people set higher standards of evidence for hypotheses that go against their current expectations. This effect, known as "disconfirmation bias", has been supported by other experiments.
A study of biased interpretation took place during the 2004 US presidential election
United States presidential election, 2004
The United States presidential election of 2004 was the United States' 55th quadrennial presidential election. It was held on Tuesday, November 2, 2004. Republican Party candidate and incumbent President George W. Bush defeated Democratic Party candidate John Kerry, the then-junior U.S. Senator...
and involved subjects who described themselves as having strong feelings about the candidates. They were shown apparently contradictory pairs of statements, either from Republican candidate George W. Bush
George W. Bush
George Walker Bush is an American politician who served as the 43rd President of the United States, from 2001 to 2009. Before that, he was the 46th Governor of Texas, having served from 1995 to 2000....
, Democratic candidate John Kerry
John Kerry
John Forbes Kerry is the senior United States Senator from Massachusetts, the 10th most senior U.S. Senator and chairman of the Senate Foreign Relations Committee. He was the presidential nominee of the Democratic Party in the 2004 presidential election, but lost to former President George W...
or a politically neutral public figure. They were also given further statements that made the apparent contradiction seem reasonable. From these three pieces of information, they had to decide whether or not each individual's statements were inconsistent. There were strong differences in these evaluations, with subjects much more likely to interpret statements by the candidate they opposed as contradictory.
In this experiment, the subjects made their judgments while in a magnetic resonance imaging
Magnetic resonance imaging
Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...
(MRI) scanner which monitored their brain activity. As subjects evaluated contradictory statements by their favored candidate, emotion
Emotion
Emotion is a complex psychophysiological experience of an individual's state of mind as interacting with biochemical and environmental influences. In humans, emotion fundamentally involves "physiological arousal, expressive behaviors, and conscious experience." Emotion is associated with mood,...
al centers of their brains were aroused. This did not happen with the statements by the other figures. The experimenters inferred that the different responses to the statements were not due to passive reasoning errors. Instead, the subjects were actively reducing the cognitive dissonance
Cognitive dissonance
Cognitive dissonance is a discomfort caused by holding conflicting ideas simultaneously. The theory of cognitive dissonance proposes that people have a motivational drive to reduce dissonance. They do this by changing their attitudes, beliefs, and actions. Dissonance is also reduced by justifying,...
induced by reading about their favored candidate's irrational or hypocritical behavior.
Biased interpretation is not restricted to emotionally significant topics. In another experiment, subjects were told a story about a theft. They had to rate the evidential importance of statements arguing either for or against a particular character being responsible. When they hypothesized that character's guilt, they rated statements supporting that hypothesis as more important than conflicting statements.
Biased memory
Even if someone has sought and interpreted evidence in a neutral manner, they may still remember it selectively to reinforce their expectations. This effect is called "selective recall", "confirmatory memory" or "access-biased memory". Psychological theories differ in their predictions about selective recall. Schema theorySchema (psychology)
A schema , in psychology and cognitive science, describes any of several concepts including:* An organized pattern of thought or behavior.* A structured cluster of pre-conceived ideas....
predicts that information matching prior expectations will be more easily stored and recalled. Some alternative approaches say that surprising information stands out more and so is more memorable. Predictions from both these theories have been confirmed in different experimental contexts, with no theory winning outright.
In one study, subjects read a profile of a woman which described a mix of introverted and extroverted behaviors. They later had to recall examples of her introversion and extroversion. One group was told this was to assess the woman for a job as a librarian, while a second group were told it was for a job in real estate sales. There was a significant difference between what these two groups recalled, with the "librarian" group recalling more examples of introversion and the "sales" groups recalling more extraverted behavior. A selective memory effect has also been shown in experiments that manipulate the desirability of personality types. In one of these, a group of subjects were shown evidence that extraverted people are more successful than introverts. Another group were told the opposite. In a subsequent, apparently unrelated, study, they were asked to recall events from their lives in which they had been either introverted or extraverted. Each group of subjects provided more memories connecting themselves with the more desirable personality type, and recalled those memories more quickly.
One study showed how selective memory can maintain belief in extrasensory perception (ESP). Believers and disbelievers were each shown descriptions of ESP experiments. Half of each group were told that the experimental results supported the existence of ESP, while the others were told they did not. In a subsequent test, subjects recalled the material accurately, apart from believers who had read the non-supportive evidence. This group remembered significantly less information and some of them incorrectly remembered the results as supporting ESP.
Polarization of opinion
When people with opposing views interpret new information in a biased way, their views can move even further apart. This is called "attitude polarization". The effect was demonstrated by an experiment that involved drawing a series of red and black balls from one of two concealed "bingo baskets". Subjects knew that one basket contained 60% black and 40% red balls; the other, 40% black and 60% red. The experimenters looked at what happened when balls of alternating color were drawn in turn, a sequence that does not favor either basket. After each ball was drawn, subjects in one group were asked to state out loud their judgments of the probability that the balls were being drawn from one or the other basket. These subjects tended to grow more confident with each successive draw—whether they initially thought the basket with 60% black balls or the one with 60% red balls was the more likely source, their estimate of the probability increased. Another group of subjects were asked to state probability estimates only at the end of a sequence of drawn balls, rather than after each ball. They did not show the polarization effect, suggesting that it does not necessarily occur when people simply hold opposing positions, but rather when they openly commit to them.Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
strongly with their initial attitudes. In later experiments, subjects also reported their opinions becoming more extreme in response to ambiguous information. However, comparisons of their attitudes before and after the new evidence showed no significant change, suggesting that the self-reported changes might not be real. Based on these experiments, Deanna Kuhn and Joseph Lao concluded that polarization is a real phenomenon but far from inevitable, only happening in a small minority of cases. They found that it was prompted not only by considering mixed evidence, but by merely thinking about the topic.
Charles Taber and Milton Lodge argued that the Stanford team's result had been hard to replicate because the arguments used in later experiments were too abstract or confusing to evoke an emotional response. The Taber and Lodge study used the emotionally charged topics of gun control
Gun politics
Gun politics addresses safety issues and ideologies related to firearms through criminal and noncriminal use. Gun politics deals with rules, regulations, and restrictions on the use, ownership, and distribution of firearms.-National sovereignty:...
and affirmative action
Affirmative action
Affirmative action refers to policies that take factors including "race, color, religion, gender, sexual orientation or national origin" into consideration in order to benefit an underrepresented group, usually as a means to counter the effects of a history of discrimination.-Origins:The term...
. They measured the attitudes of their subjects towards these issues before and after reading arguments on each side of the debate. Two groups of subjects showed attitude polarization; those with strong prior opinions and those who were politically knowledgeable. In part of this study, subjects chose which information sources to read, from a list prepared by the experimenters. For example they could read the National Rifle Association
National Rifle Association
The National Rifle Association of America is an American non-profit 501 civil rights organization which advocates for the protection of the Second Amendment of the United States Bill of Rights and the promotion of firearm ownership rights as well as marksmanship, firearm safety, and the protection...
's and the Brady Anti-Handgun Coalition
Brady Campaign
The Brady Campaign to Prevent Gun Violence and the Brady Center to Prevent Gun Violence are affiliated non-profit organizations in the United States. They are named after James Brady who was permanently disabled as a result of an assassination attempt on U.S. President Ronald Reagan in 1981...
's arguments on gun control. Even when instructed to be even-handed, subjects were more likely to read arguments that supported their existing attitudes. This biased search for information correlated well with the polarization effect.
Persistence of discredited beliefs
Confirmation biases can be used to explain why some beliefs remain when the initial evidence for them is removed. This belief perseverance effect has been shown by a series of experiments using what is called the "debriefing paradigm": subjects examine faked evidence for a hypothesis, their attitude change is measured, then they learn that the evidence was fictitious. Their attitudes are then measured once more to see if their belief returns to its previous level.A typical finding is that at least some of the initial belief remains even after a full debrief. In one experiment, subjects had to distinguish between real and fake suicide notes. The feedback was random: some were told they had done well while others were told they had performed badly. Even after being fully debriefed, subjects were still influenced by the feedback. They still thought they were better or worse than average at that kind of task, depending on what they had initially been told.
In another study, subjects read job performance ratings of two firefighters, along with their responses to a risk aversion
Risk aversion
Risk aversion is a concept in psychology, economics, and finance, based on the behavior of humans while exposed to uncertainty....
test. These fictional data were arranged to show either a negative or positive association
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
between risk-taking attitudes and job success. Even if these case studies had been true, they would have been scientifically poor evidence. However, the subjects found them subjectively persuasive. When the case studies were shown to be fictional, subjects' belief in a link diminished, but around half of the original effect remained. Follow-up interviews established that the subjects had understood the debriefing and taken it seriously. Subjects seemed to trust the debriefing, but regarded the discredited information as irrelevant to their personal belief.
Preference for early information
Experiments have shown that information is weighted more strongly when it appears early in a series, even when the order is unimportant. For example, people form a more positive impression of someone described as "intelligent, industrious, impulsive, critical, stubborn, envious" than when they are given the same words in reverse order. This irrational primacy effect is independent of the primacy effect in memorySerial position effect
The serial position effect, a term coined by Hermann Ebbinghaus through studies he performed on himself, refers to the finding that recall accuracy varies as a function of an item's position within a study list . When asked to recall a list of items in any order , people tend to begin recall with...
in which the earlier items in a series leave a stronger memory trace. Biased interpretation offers an explanation for this effect: seeing the initial evidence, people form a working hypothesis that affects how they interpret the rest of the information.
One demonstration of irrational primacy involved colored chips supposedly drawn from two urns. Subjects were told the color distributions of the urns, and had to estimate the probability of a chip being drawn from one of them. In fact, the colors appeared in a pre-arranged order. The first thirty draws favored one urn and the next thirty favored the other. The series as a whole was neutral, so rationally, the two urns were equally likely. However, after sixty draws, subjects favored the urn suggested by the initial thirty.
Another experiment involved a slide show of a single object, seen as just a blur at first and in slightly better focus with each succeeding slide. After each slide, subjects had to state their best guess of what the object was. Subjects whose early guesses were wrong persisted with those guesses, even when the picture was sufficiently in focus that other people could readily identify the object.
Illusory association between events
Illusory correlationIllusory correlation
Illusory correlation is the phenomenon of seeing the relationship one expects in a set of data even when no such relationship exists. When people form false associations between membership in a statistical minority group and rare behaviors, this would be a common example of illusory correlation...
is the tendency to see non-existent correlations in a set of data. This tendency was first demonstrated in a series of experiments in the late 1960s. In one experiment, subjects read a set of psychiatric case studies, including responses to the Rorschach inkblot test
Rorschach inkblot test
The Rorschach test is a psychological test in which subjects' perceptions of inkblots are recorded and then analyzed using psychological interpretation, complex algorithms, or both. Some psychologists use this test to examine a person's personality characteristics and emotional functioning...
. They reported that the homosexual men in the set were more likely to report seeing buttocks, anuses or sexually ambiguous figures in the inkblots. In fact the case studies were fictional and, in one version of the experiment, had been constructed so that the homosexual men were less likely to report this imagery. In a survey, a group of experienced psychoanalysts reported the same set of illusory associations with homosexuality.
Another study recorded the symptoms experienced by arthritic patients, along with weather conditions over a 15-month period. Nearly all the patients reported that their pains were correlated with weather conditions, although the real correlation was zero.
This effect is a kind of biased interpretation, in that objectively neutral or unfavorable evidence is interpreted to support existing beliefs. It is also related to biases in hypothesis-testing behavior. In judging whether two events, such as illness and bad weather, are correlated, people rely heavily on the number of positive-positive cases: in this example, instances of both pain and bad weather. They pay relatively little attention to the other kinds of observation (of no pain and/or good weather). This parallels the reliance on positive tests in hypothesis testing. It may also reflect selective recall, in that people may have a sense that two events are correlated because it is easier to recall times when they happened together.
| Days | Rain | No rain |
|---|---|---|
| Arthritis | 14 | 6 |
| No arthritis | 7 | 2 |
In the above fictional example, arthritic symptoms are more likely on days with no rain. However, people are likely to focus on the relatively large number of days which have both rain and symptoms. By concentrating on one cell of the table rather than all four, people can misperceive the relationship, in this case associating rain with arthritic symptoms.
History
Informal observation
Before psychological research on confirmation bias, the phenomenon had been observed anecdotally by writers, including the Greek historian ThucydidesThucydides
Thucydides was a Greek historian and author from Alimos. His History of the Peloponnesian War recounts the 5th century BC war between Sparta and Athens to the year 411 BC...
(c. 460 BC – c. 395 BC), Italian poet Dante Alighieri
Dante Alighieri
Durante degli Alighieri, mononymously referred to as Dante , was an Italian poet, prose writer, literary theorist, moral philosopher, and political thinker. He is best known for the monumental epic poem La commedia, later named La divina commedia ...
(1265–1321), English philosopher and scientist Francis Bacon
Francis Bacon
Francis Bacon, 1st Viscount St Albans, KC was an English philosopher, statesman, scientist, lawyer, jurist, author and pioneer of the scientific method. He served both as Attorney General and Lord Chancellor of England...
(1561–1626), and Russian author Leo Tolstoy
Leo Tolstoy
Lev Nikolayevich Tolstoy was a Russian writer who primarily wrote novels and short stories. Later in life, he also wrote plays and essays. His two most famous works, the novels War and Peace and Anna Karenina, are acknowledged as two of the greatest novels of all time and a pinnacle of realist...
(1828–1910). Thucydides, in the History of the Peloponnesian War
History of the Peloponnesian War
The History of the Peloponnesian War is an account of the Peloponnesian War in Ancient Greece, fought between the Peloponnesian League and the Delian League . It was written by Thucydides, an Athenian general who served in the war. It is widely considered a classic and regarded as one of the...
wrote, "it is a habit of mankind ... to use sovereign reason to thrust aside what they do not fancy." In the Divine Comedy, St. Thomas Aquinas cautions Dante when they meet in Paradise, "opinion—hasty—often can incline to the wrong side, and then affection for one's own opinion binds, confines the mind." Bacon, in the Novum Organum
Novum Organum
The Novum Organum, full original title Novum Organum Scientiarum, is a philosophical work by Francis Bacon, written in Latin and published in 1620. The title translates as new instrument, i.e. new instrument of science. This is a reference to Aristotle's work Organon, which was his treatise on...
, wrote,
Bacon said that biased assessment of evidence drove "all superstitions, whether in astrology, dreams, omens, divine judgments or the like". In his essay "What Is Art?
What Is Art?
"What Is Art?" is an essay by Leo Tolstoy in which he argues against numerous aesthetic theories which define art in terms of the good, truth, and especially beauty...
", Tolstoy wrote,
Wason's research on hypothesis-testing
The term "confirmation bias" was coined by English psychologist Peter WasonPeter Cathcart Wason
Peter Cathcart Wason was a cognitive psychologist, who worked on the psychology of reason. He made great progress in explaining why people make certain consistent mistakes in logical reasoning...
. For an experiment published in 1960, he challenged subjects to identify a rule applying to triples of numbers. At the outset, they were told that (2,4,6) fits the rule. Subjects could generate their own triples and the experimenter told them whether or not each triple conformed to the rule.
While the actual rule was simply "any ascending sequence", the subjects had a great deal of difficulty in arriving at it, often announcing rules that were far more specific, such as "the middle number is the average of the first and last". The subjects 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 fit this rule, such as (11,13,15) rather than a triple that violates it, such as (11,12,19).
Wason accepted falsificationism, according to which a scientific test of a hypothesis is a serious attempt to falsify it. He interpreted his results as showing a preference for confirmation over falsification, hence the term "confirmation bias".Wason also used the term "verification bias". Wason also used confirmation bias to explain the results of his selection task
Wason selection task
Devised in 1966 by Peter Cathcart Wason, the Wason selection task, one of the most famous tasks in the psychology of reasoning, is a logic puzzle which is formally equivalent to the following question:...
experiment. In this task, subjects are given partial information about a set of objects, and have to specify what further information they would need to tell whether or not a conditional rule
Material conditional
The material conditional, also known as material implication, is a binary truth function, such that the compound sentence p→q is logically equivalent to the negative compound: not . A material conditional compound itself is often simply called a conditional...
("If A, then B") applies. It has been found repeatedly that people perform badly on various forms of this test, in most cases ignoring information that could potentially refute the rule.
Klayman and Ha's critique
A 1987 paper by Joshua Klayman and Young-Won Ha argued that the Wason experiments had not actually demonstrated a bias towards confirmation. Instead, Klayman and Ha interpreted the results in terms of a tendency to make tests that are consistent with the working hypothesis. They called this the "positive test strategy". This strategy is an example of a heuristicHeuristic
Heuristic refers to experience-based techniques for problem solving, learning, and discovery. Heuristic methods are used to speed up the process of finding a satisfactory solution, where an exhaustive search is impractical...
: a reasoning shortcut that is imperfect but easy to compute. Klayman and Ha used Bayesian probability
Bayesian probability
Bayesian probability is one of the different interpretations of the concept of probability and belongs to the category of evidential probabilities. The Bayesian interpretation of probability can be seen as an extension of logic that enables reasoning with propositions, whose truth or falsity is...
and information theory
Information theory
Information theory is a branch of applied mathematics and electrical engineering involving the quantification of information. Information theory was developed by Claude E. Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and...
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. 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. Subjects had much more success with this version of the experiment.
In light of this and other critiques, the focus of research moved away from confirmation versus falsification to examine 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.
Explanations
Confirmation bias is often described as a result of automatic processing. Individuals do not use deceptive strategies to fake data, but forms of information processing that take place more or less unintentionally. According to Robert Maccoun, most biased evidence processing occurs unintentionally through a combination of both "hot" (i.e., motivated) and "cold" (i.e., cognitive) mechanisms.Cognitive explanations for confirmation bias are based on limitations in people's ability to handle complex tasks, and the shortcuts, called "heuristics", that they use. For example, people may judge the reliability of evidence by using the availability heuristic
Availability heuristic
The availability heuristic is a phenomenon in which people predict the frequency of an event, or a proportion within a population, based on how easily an example can be brought to mind....
, i.e. how readily a particular idea comes to mind. It is also possible that people can only focus on one thought at a time, so find it difficult to test alternative hypotheses in parallel. Another heuristic is the positive test strategy identified by Klayman and Ha, in which people test a hypothesis by examining cases where they expect a property or event to occur. This heuristic avoids the difficult or impossible task of working out how diagnostic each possible question will be. However, it is not universally reliable, so people can overlook challenges to their existing beliefs.
Motivational explanations involve an effect of desire
Desire (emotion)
Desire is a sense of longing for a person or object or hoping for an outcome. Desire is the fire that sets action aflame. The same sense is expressed by emotions such as "craving" or "hankering". When a person desires something or someone, their sense of longing is excited by the enjoyment or the...
on belief
Belief
Belief is the psychological state in which an individual holds a proposition or premise to be true.-Belief, knowledge and epistemology:The terms belief and knowledge are used differently in philosophy....
, sometimes called "wishful thinking
Wishful thinking
Wishful thinking is the formation of beliefs and making decisions according to what might be pleasing to imagine instead of by appealing to evidence, rationality or reality...
". It is known that people prefer pleasant thoughts over unpleasant ones in a number of ways: this is called the "Pollyanna principle
Pollyanna principle
The Pollyanna principle is the tendency for people to agree with positive statements describing them. The phenomenon is similar to the Forer effect. Research indicates that, at the subconscious level, our minds have a tendency to focus on the optimistic while, at the conscious level, we have a...
". Applied to argument
Argument
In philosophy and logic, an argument is an attempt to persuade someone of something, or give evidence or reasons for accepting a particular conclusion.Argument may also refer to:-Mathematics and computer science:...
s or sources of evidence
Evidence
Evidence in its broadest sense includes everything that is used to determine or demonstrate the truth of an assertion. Giving or procuring evidence is the process of using those things that are either presumed to be true, or were themselves proven via evidence, to demonstrate an assertion's truth...
, this could explain why desired conclusions are more likely to be believed true. According to experiments that manipulate the desirability of the conclusion, people demand a high standard of evidence for unpalatable ideas and a low standard for preferred ideas. In other words, they ask, "Can I believe this?" for some suggestions and, "Must I believe this?" for others. Although consistency
Consistency
Consistency can refer to:* Consistency , the psychological need to be consistent with prior acts and statements* "Consistency", an 1887 speech by Mark Twain...
is a desirable feature of attitudes, an excessive drive for consistency is another potential source of bias because it may prevent people from neutrally evaluating new, surprising information. Social psychologist Ziva Kunda
Ziva Kunda
Ziva Kunda was a social psychologist well-known for her work in social cognition and motivated reasoning.-Early life:Kunda obtained her Ph.D. at the University of Michigan and was the author of the textbook .-Career:...
combines the cognitive and motivational theories, arguing that motivation creates the bias, but cognitive factors determine the size of the effect.
Explanations in terms of cost-benefit analysis
Cost-benefit analysis
Cost–benefit analysis , sometimes called benefit–cost analysis , is a systematic process for calculating and comparing benefits and costs of a project for two purposes: to determine if it is a sound investment , to see how it compares with alternate projects...
assume that people do not just test hypotheses in a disinterested way, but assess the costs of different errors. Using ideas from evolutionary psychology
Evolutionary psychology
Evolutionary psychology is an approach in the social and natural sciences that examines psychological traits such as memory, perception, and language from a modern evolutionary perspective. It seeks to identify which human psychological traits are evolved adaptations, that is, the functional...
, James Friedrich suggests that people do not primarily aim at truth
Truth
Truth has a variety of meanings, such as the state of being in accord with fact or reality. It can also mean having fidelity to an original or to a standard or ideal. In a common usage, it also means constancy or sincerity in action or character...
in testing hypotheses, but try to avoid the most costly errors. For example, employers might ask one-sided questions in job interviews because they are focused on weeding out unsuitable candidates. Yaacov Trope and Akiva Liberman's refinement of this theory assumes that people compare the two different kinds of error: accepting a false hypothesis or rejecting a true hypothesis. For instance, someone who underestimates a friend's honesty might treat him or her suspiciously and so undermine the friendship. Overestimating the friend's honesty may also be costly, but less so. In this case, it would be rational to seek, evaluate or remember evidence of their honesty in a biased way. When someone gives an initial impression of being introverted or extraverted, questions that match that impression come across as more empathic. This suggests that when talking to someone who seems to be an introvert, it is a sign of better social skills
Social skills
A social skill is any skill facilitating interaction and communication with others. Social rules and relations are created, communicated, and changed in verbal and nonverbal ways. The process of learning such skills is called socialization...
to ask, "Do you feel awkward in social situations?" rather than, "Do you like noisy parties?" The connection between confirmation bias and social skills was corroborated by a study of how college students get to know other people. Highly self-monitoring students, who are more sensitive to their environment and to social norms, asked more matching questions when interviewing a high-status staff member than when getting to know fellow students.
In finance
Confirmation bias can lead investors to be overconfident, ignoring evidence that their strategies will lose money. In studies of political stock marketsElection Stock Market
Election stock markets are financial markets in which the ultimate values of the contracts being traded are based on the outcome of elections. Participants invest their own funds, buy and sell listed contracts, earn profits and bear the risk of losing money...
, investors made more profit when they resisted bias. For example, participants who interpreted a candidate's debate performance in a neutral rather than partisan way were more likely to profit. To combat the effect of confirmation bias, investors can try to adopt a contrary viewpoint "for the sake of argument". One such technique involves imagining that their investments have collapsed and asking why this might happen.
In physical and mental health
Raymond Nickerson, a psychologist, blames confirmation bias for the ineffective medical procedures that were used for centuries before the arrival of scientific medicineHistory of medicine
All human societies have medical beliefs that provide explanations for birth, death, and disease. Throughout history, illness has been attributed to witchcraft, demons, astral influence, or the will of the gods...
. If a patient recovered, medical authorities counted the treatment as successful, rather than looking for alternative explanations such as that the disease had run its natural course. Biased assimilation is a factor in the modern appeal of alternative medicine
Alternative medicine
Alternative medicine is any healing practice, "that does not fall within the realm of conventional medicine." It is based on historical or cultural traditions, rather than on scientific evidence....
, whose proponents are swayed by positive anecdotal evidence
Anecdotal evidence
The expression anecdotal evidence refers to evidence from anecdotes. Because of the small sample, there is a larger chance that it may be true but unreliable due to cherry-picked or otherwise unrepresentative of typical cases....
but treat scientific evidence hyper-critically.
Cognitive therapy
Cognitive therapy
Cognitive behavioral therapy is a psychotherapeutic approach: a talking therapy. CBT aims to solve problems concerning dysfunctional emotions, behaviors and cognitions through a goal-oriented, systematic procedure in the present...
was developed by Aaron T. Beck
Aaron T. Beck
Aaron Temkin Beck is an American psychiatrist and a professor emeritus in the department of psychiatry at the University of Pennsylvania. He is widely regarded as the father of cognitive therapy, and his pioneering theories are widely used in the treatment of clinical depression...
in the early 1960s and has become a popular approach. According to Beck, biased information processing is a factor in depression
Depression (mood)
Depression is a state of low mood and aversion to activity that can affect a person's thoughts, behaviour, feelings and physical well-being. Depressed people may feel sad, anxious, empty, hopeless, helpless, worthless, guilty, irritable, or restless...
. His approach teaches people to treat evidence impartially, rather than selectively reinforcing negative outlooks. Phobias and hypochondria
Hypochondria
Hypochondriasis or hypochondria refers to excessive preoccupation or worry about having a serious illness. This debilitating condition is the result of an inaccurate perception of the body’s condition despite the absence of an actual medication condition...
have also been shown to involve confirmation bias for threatening information.
In politics and law
Mock trial
A Mock Trial is an act or imitation trial. It is similar to a moot court, but mock trials simulate lower-court trials, while moot court simulates appellate court hearings. Attorneys preparing for a real trial might use a mock trial consisting of volunteers as role players to test theories or...
s. Both inquisitorial
Inquisitorial system
An inquisitorial system is a legal system where the court or a part of the court is actively involved in investigating the facts of the case, as opposed to an adversarial system where the role of the court is primarily that of an impartial referee between the prosecution and the defense...
and adversarial
Adversarial system
The adversarial system is a legal system where two advocates represent their parties' positions before an impartial person or group of people, usually a jury or judge, who attempt to determine the truth of the case...
criminal justice systems are affected by confirmation bias.
Confirmation bias can be a factor in creating or extending conflicts, from emotionally charged debates to wars: by interpreting the evidence in their favor, each opposing party can become overconfident that it is in the stronger position. On the other hand, confirmation bias can result in people ignoring or misinterpreting the signs of an imminent or incipient conflict. For example, psychologists Stuart Sutherland
Stuart Sutherland
Norman Stuart Sutherland , always known professionally as Stuart Sutherland, was a British psychologist and writer....
and Thomas Kida have each argued that US Admiral Husband E. Kimmel
Husband E. Kimmel
Husband Edward Kimmel was a four-star admiral in the United States Navy. He served as Commander-in-chief, U.S. Pacific Fleet at the time of the Japanese attack on Pearl Harbor. Because of the attack, he was removed from office and was reduced to his permanent two-star rank of rear admiral...
showed confirmation bias when playing down the first signs of the Japanese attack on Pearl Harbor
Attack on Pearl Harbor
The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...
.
A two-decade study of political pundits by Philip E. Tetlock
Philip E. Tetlock
Philip E. Tetlock is Leonore Annenberg University Professor of Psychology at the University of Pennsylvania. He has also written several non-fiction books on politics, including Counterfactual Thought Experiments in World Politics and "Expert Political Judgment: How Good Is It? How Can We...
found that, on the whole, their predictions were not much better than chance. Tetlock divided experts into "foxes" who maintained multiple hypotheses, and "hedgehogs" who were more dogmatic. In general, the hedgehogs were much less accurate. Tetlock blamed their failure on confirmation bias—specifically, their inability to make use of new information that contradicted their existing theories.
In the paranormal
One factor in the appeal of psychicPsychic
A psychic is a person who professes an ability to perceive information hidden from the normal senses through extrasensory perception , or is said by others to have such abilities. It is also used to describe theatrical performers who use techniques such as prestidigitation, cold reading, and hot...
"readings" is that listeners apply a confirmation bias which fits the psychic's statements to their own lives. By making a large number of ambiguous statements in each sitting, the psychic gives the client more opportunities to find a match. This is one of the techniques of cold reading
Cold reading
Cold reading is a series of techniques used by mentalists, psychics, fortune-tellers, illusionists, and con artists to determine or express details about another person, often in order to convince them that the reader knows much more about a subject than they actually do...
, with which a psychic can deliver a subjectively impressive reading without any prior information about the client. Investigator James Randi
James Randi
James Randi is a Canadian-American stage magician and scientific skeptic best known as a challenger of paranormal claims and pseudoscience. Randi is the founder of the James Randi Educational Foundation...
compared the transcript of a reading to the client's report of what the psychic had said, and found that the client showed a strong selective recall of the "hits".
As a "striking illustration" of confirmation bias in the real world, Nickerson mentions numerological pyramidology
Pyramidology
Pyramidology is a term used, sometimes disparagingly, to refer to various pseudoscientific speculations regarding pyramids, most often the Giza Necropolis and the Great Pyramid of Giza in Egypt...
: the practice of finding meaning in the proportions of the Egyptian pyramids. There are many different length measurements that can be made of, for example, the Great Pyramid of Giza
Great Pyramid of Giza
The Great Pyramid of Giza is the oldest and largest of the three pyramids in the Giza Necropolis bordering what is now El Giza, Egypt. It is the oldest of the Seven Wonders of the Ancient World, and the only one to remain largely intact...
and many ways to combine or manipulate them. Hence it is almost inevitable that people who look at these numbers selectively will find superficially impressive correspondences, for example with the dimensions of the Earth.
In scientific procedure
A distinguishing feature of scientific thinkingScience
Science is a systematic enterprise that builds and organizes knowledge in the form of testable explanations and predictions about the universe...
is the search for falsifying as well as confirming evidence. However, many times in the history of science
History of science
The history of science is the study of the historical development of human understandings of the natural world and the domains of the social sciences....
, scientists have resisted new discoveries by selectively interpreting or ignoring unfavorable data. Previous research has shown that the assessment of the quality of scientific studies seems to be particularly vulnerable to confirmation bias. It has been found several times that scientists rate studies that report findings consistent with their prior beliefs more favorably than studies reporting findings inconsistent with their previous beliefs. However, assuming that the research question is relevant, the experimental design adequate and the data are clearly and comprehensively described, the found results should be of importance to the scientific community and should not be viewed prejudicially—regardless of whether they conform to current theoretical predictions. Confirmation bias may thus be especially harmful to objective evaluations regarding nonconforming results, since biased individuals may regard opposing evidence to be weak in principle and give little serious thought to revising their beliefs. Scientific innovators often meet with resistance from the scientific community, and research presenting controversial results frequently receives harsh peer review. In the context of scientific research, confirmation biases can sustain theories or research programs in the face of inadequate or even contradictory evidence; the field of parapsychology
Parapsychology
The term parapsychology was coined in or around 1889 by philosopher Max Dessoir, and originates from para meaning "alongside", and psychology. The term was adopted by J.B. Rhine in the 1930s as a replacement for the term psychical research...
has been particularly affected. An experimenter's confirmation bias can potentially affect which data are reported. Data that conflict with the experimenter's expectations may be more readily discarded as unreliable, producing the so-called file drawer effect
Publication bias
Publication bias is the tendency of researchers, editors, and pharmaceutical companies to handle the reporting of experimental results that are positive differently from results that are negative or inconclusive, leading to bias in the overall published literature...
. To combat this tendency, scientific training teaches ways to avoid bias. Experimental designs involving randomization and double blind trials, along with the social process of peer review
Peer review
Peer review is a process of self-regulation by a profession or a process of evaluation involving qualified individuals within the relevant field. Peer review methods are employed to maintain standards, improve performance and provide credibility...
, are thought to mitigate the effect of individual scientists' biases, although it has been argued that such biases can play a role in the peer review process itself.
In self-image
Social psychologists have identified two tendencies in the way people seek or interpret information about themselves. Self-verification is the drive to reinforce the existing self-image and self-enhancementSelf-enhancement
Self-enhancement is a type of motivation that works to make people feel good about themselves and to maintain self-esteem. This motive becomes especially prominent in situations of threat, failure or blows to one's self-esteem...
is the drive to seek positive feedback. Both are served by confirmation biases. In experiments where people are given feedback that conflicts with their self-image, they are less likely to attend to it or remember it than when given self-verifying feedback. They reduce the impact of such information by interpreting it as unreliable. Similar experiments have found a preference for positive feedback, and the people who give it, over negative feedback.
External links
- Skeptic's Dictionary: confirmation bias by Robert T. Carroll
- Teaching about confirmation bias, class handout and instructor's notes by K. H. Grobman
- Confirmation bias learning object, interactive number triples exercise by Rod McFarland, Simon Fraser University
- Brief summary of the 1979 Stanford assimilation bias study by Keith Rollag, Babson College
- "Morton's demon", Usenet post by Glenn Morton, February 2, 2002