Illusory Correlation Chapman and Chapman (1967) First Demon- Strated the Existence of Illusory Correlation in Ashley L

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Illusory Correlation Chapman and Chapman (1967) first demon- strated the existence of illusory correlation in Ashley L. Watts, Sarah Francis Smith, the domain of psychological assessment. They and Scott O. Lilienfeld asked clinical psychologists to list the charac- Emory University, U.S.A. teristics (“signs”) of various Draw-a-Person (DAP; Machover, 1949) protocols that are Many individuals hold strong, often unyield- associated with specific psychiatric symptoms ing, convictions about the association between and personality traits. The DAP is a widely occurrences that have been shown to be sta- used projective technique that asks partici- tistically unrelated, such as the full moon pants to draw three people—a man, a woman, and strange behavior, or joint pain and rainy and themselves—which purportedly allows weather. Indeed, these and many other ven- clinicians to infer a wide range of normal erable legends are held by the masses in the and abnormal personality traits. Chapman face of clear contrary evidence (Redelmeier & and Chapman found that clinicians exhibited Tversky, 1996). strong agreement on certain pairings of DAP Why do many of us perceive statistical asso- signsandcertainsymptomsorpersonality ciations between certain events when these traits. For example, 91% of clinicians reported associations are objectively absent? The answer that atypical eyes on the DAP tend to be a valid is of substantial importance to clinical psy- indicator of suspiciousness, and 82% of clini- chology and allied fields. Clinical psychologists cians agreed that a large or emphasized head dub this phenomenon illusory correlation is a valid indicator of intelligence. Chapman (Chapman & Chapman, 1967, 1969). More and Chapman observed that these associations specifically, an illusory correlation is reflect potent associative linkages between certain drawing signs and certain indicators the report by observers of a correlation between of psychological disturbance. For example, as twoclassesofevents,which,inreality,(a)arenot clinical psychologist Paul Meehl (1920–2003) correlated, or (b) are correlated to a lesser extent noted, paranoid people are often characterized than reported, or (c) are correlated in the opposite by wide-open eyes. Yet these intuitive relations, direction from that which is reported. (Chapman, which mirror those found in DAP manuals, 1967, p. 151) had been disconfirmed in many previous Psychologicalresearchdemonstratesthat studies. humans tend to be poor at estimating the Inthesecondpartofthestudy,theChapmans statistical relations among events; this faulty presented students with DAP protocols along statistical barometer can predispose us to with pairs of symptom statements, and asked illusory correlations (Dawes, 1989). them to inspect the pictures and statements carefully. For example, a drawing presented Illusory Correlation and Clinical to a participant was attached to two symptom Assessment statements, such as “The man who drew this is either (a) suspicious of other people or (b) Although illusory correlation is a domain-gen- worried about how manly he is.” The pairs of eral phenomenon, Chapman (1967) believed symptom statements were drawn from the six that it bears especially important implications symptoms that the clinicians had listed as DAP for clinical settings, such as biases (systematic correlates;thepairsofstatementswereran- errors)inclinicaljudgment.Inaclassicstudy, domly assigned to each drawing so that each

The Encyclopedia of Clinical Psychology, First Edition. Edited by Robin L. Cautin and Scott O. Lilienfeld. © 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc. DOI: 10.1002/9781118625392.wbecp573 2 ILLUSORY CORRELATION symptom statement appeared only once with likely that strong semantic associations persist each of the drawings. After viewing all of the between some scale labels and test responses drawings, the researchers asked participants (e.g., Depression and “feels blue or sad”). The which characteristics of the drawings were authors hypothesized that many clinicians associated with which psychological charac- continued to use the original labels, which may teristics. Remarkably, these results mirrored lead to illusory correlation when judges are the relations perceived by clinical psychol- asked to infer relations between MMPI scales ogists (e.g., broad shoulders and manliness, and psychiatric symptoms. atypical eyes and suspiciousness). That is, the Dowling and Graham tested this hypothesis undergraduate participants had “recaptured” in a twofold manner. First, they compiled the identical illusory associates perceived by a pool of items in which an MMPI scale clinicians. name was paired with two of 10 behavioral In a follow-up study, Chapman and Chap- statements (e.g., often complains about his man (1969) replicated their findings using a health, sleeps whenever possible, and keeps his different projective task, the perennially popu- clothes neat). Each statement possessed some lar Rorschach Inkblot Test (Rorschach, 1927). semantic association with at least one of the They sought to identify illusory correlations MMPI scales, but not necessarily the scale with between Rorschach responses and homosex- which it was paired. To ensure that there was uality,whichatthetimewasadiagnosticcat- no actual relation between the MMPI scale egory in DSM-II (American Psychiatric Asso- and the behavioral statements, the researchers ciation, 1968). As predicted, an overwhelming chosestatementsthatwerenotstatistically majority of clinicians reported that a number of associated with any clinical scale more than specific Rorschach responses were associated another. Each subject received a brief intro- with homosexuality (e.g., responses referring to duction to the MMPI, including the names of the anus, feminine clothing, genitals, or sexual the 10 scales; nevertheless, they received no ambiguity). As in the Chapman and Chapman descriptions of these scales. Next, one group of (1967) study, the researchers asked undergraduate students, who had completed a course graduates to render judgments after viewing on the MMPI, and one group of undergrad- Rorschach protocols paired with personality uate students each studied the pool of items. statements; the personality statements were Later, they indicated with which MMPI scale rigged so that there was no statistical relation each of the 10 behavioral statements was most between the card and the statement. Despite associated. the absence of any statistical association Despite the fact that the behavioral state- between the Rorschach cards and the symptom ments were no more likely to co-occur with statements, undergraduates, like clinicians, a specific MMPI scale over any other, under- reported that the aforementioned signs (e.g., graduates reported that certain behavioral anus, feminine clothing, etc.) were indicators of statements co-occurred with certain MMPI homosexuality, despite the fact that the actual scales six out of 10 times. Interestingly, graduate correlations between the signs and homosexu- students reported a significant co-occurrence ality in the stimulus materials were zero. for nine out of 10 statements, suggesting even Dowling and Graham (1976) extended higher levels of illusory correlation. Dowling work on illusory correlation to more objective and Graham’s findings demonstrate that illu- assessment techniques, namely, the widely sory correlation is not limited to projective used Minnesota Multiphasic Personality techniques, and suggest that the tendency Inventory (MMPI; Hathaway & McKinley, to perceive relations between uncorrelated 1943). Despite the fact that the MMPI’s clin- phenomena does not necessarily decrease with ical scale labels were replaced with numbers clinical experience. More broadly, findings (e.g., Psychopathic deviate with 4), it seems concerning illusory correlation have been ILLUSORY CORRELATION 3 replicated using different assessment tasks and (Douglas, Guy, & Hart, 2009), mentally ill different groups of participants (see Starr & individuals account for a negligible portion of Katkin, 1969, for similar findings regarding the violent crimes committed (Quinsey, Harris, Rotter Incomplete Sentences Blank task; and Rice, & Cormier, 2006). Furthermore, the link King & Koehler, 2000, for findings regarding between mental illness and violence is mod- graphology, or handwriting analysis). erated by abuse of drugs and alcohol (Fazel, Gulati, Linsell, Geddes, & Grann, 2009). Fazel Illusory Correlation and Erroneous and colleagues (2009) found that the relation Cultural Beliefs between psychosis and risk was due largely or entirely to co-occurring substance use The implications of illusory correlation extend disorders. The increased risk for violence in well beyond psychological assessment. Indeed, psychotic individuals was not significantly dif- many widespread cultural beliefs reflect illu- ferent from the risk for violence in individuals sory correlations. For example, numerous with substance use disorders alone. Although superstitions, such as linkages between the the reasons for these findings are unknown, number 13 and negative outcomes, are illu- certain illicit substances may trigger violent sory correlations. Another striking illusory behavior by impairing judgment or decreasing correlation is the “lunar lunacy effect” or inhibitions. Additionally, among individuals “Transylvania effect”: the purported relation with severe mental illness, substance abuse may between the full moon and mental illness, exacerbate psychiatric symptoms (e.g., para- violence, and odd behavior (Lilienfeld & noia and hostility). On balance, although some Arkowitz, 2009). One survey (Rotton & Kelly, noteworthy examples (e.g., James Holmes, the 1985a) revealed that 49.4% of college students 2012 Aurora, Colorado movie theater shooter) believe that there is a statistical association fit our conception of violent, mentally ill per- between the full moon and strange occur- petrators, many or most of us substantially rences (e.g., violent crimes and psychiatric overestimatetheriskofviolenceamongthe hospital admissions). Yet data consistently sug- mentally ill. gest that this belief is unwarranted. Rotton and More broadly, many racial stereotypes reflect Kelly (1985b) conducted a meta-analysis of 37 illusory correlation. One kind of stereotype studies examining the relation between the full involves the belief that a certain behavior moon and a plethora of undesirable behaviors (e.g., violence, laziness, or arrogance) is more (e.g., homicides, suicides, and disturbances in specific to one ethnic or cultural group than psychiatric settings) and found no evidence another, even when this association does not that people behave any more aberrantly during reflect reality. In such cases, observers per- one phase of the moon than another (see also ceive a statistical association between ethnic Kelly, Rotton, & Culver, 1996). or cultural group membership and specific All too present in popular culture, and even behaviors when this association is largely or among clinical psychologists, is the miscon- entirely nonexistent. ception that mentally ill individuals are at Illusory correlation may also predispose to markedly heightened risk for violence. A large mistaken inferences concerning the causes of national survey conducted in 2006 revealed psychopathology. Take the widely publicized that 60% of Americans believed that individ- and highly contentious notion that vaccines uals with schizophrenia are likely to engage in increase the risk for autism or other neurode- violent behavior; 32% believed that individuals velopmental disorders (Wakefield et al., 1998). with major depression are likely to do so. Survey data suggest that 24% of individuals These beliefs rarely reflect reality. Although believe that vaccines cause autism (Florida meta-analyses reveal a weak to modest relation Institute of Technology, 2008). This hypothesis between severe mental illness and violence originated with a now-discredited research 4 ILLUSORY CORRELATION study published in 1998 by British pediatrician snakes or spiders, depending on the condition) Andrew Wakefield and his colleagues, which and fear-neutral slides (images of mushrooms described eight children whose symptoms of and flowers). The slides were paired with one autism emerged within a month of receiving of three outcomes: a tone, a shock, or nothing. themeasles–mumps–rubella (MMR)vaccine. At the end of the slide presentation, Tomarken From these observations, Wakefield and his et al. asked participants to rate the percentage coauthors hypothesized that the MMR vaccine of trials for which each category of slides was adversely affected neurodevelopment and in paired with each outcome (e.g., the percentage turn boosted the risk of autism. of trials for which they believed a snake image Although Wakefield’s observations have not was paired with a shock). As in the Chapmans’ withstood scientific scrutiny, it remains pop- studies, there was no correlation between any ular largely because it makes intuitive sense. categoryofslideandanytypeofoutcome. Indeed, illusory correlation may be partially Tomarken and colleagues (1989) found that to blame. Because children typically receive high-fear subjects overestimated the associa- the MMR vaccine between the ages of 1 and tion between fear-relevant stimuli and aversive 2—around the same time the first symptoms of outcomes (e.g., shock) despite the fact that the autism typically become apparent—an associ- associations between all stimuli and outcomes ation between the two events seems plausible. were equal. Moreover, high-fear subjects’ esti- Nevertheless, there is no compelling evidence mates of the relation between fear-relevant for a link between autism and vaccinations. stimuli and negative outcomes (e.g., shock) A comprehensive review by the Institute of were significantly greater than their estimates Medicine in 2004 found no relation between of the relation between fear-relevant slides and vaccines and autism (see Plotkin, Gerber, & nonaversive outcomes (e.g., tone or nothing). Offit, 2009, and Orenstein, Paulson, Brady, Additionally, high-fear subjects’ estimates of Cooper, & Seib, 2013, for more recent negative the relation between fear-relevant stimuli and evidence). Moreover, there is no evidence that shock were significantly higher than those of stronger doses of vaccines are associated with low-fear subjects. The findings of the Tomarken higher autism rates than are weaker doses etal.study,whichhavesincebeenreplicated (Hviid, Stellfeld, Wohlfahrt, & Melbye, 2003). (see Mineka & Sutton, 1992, for a review), indicate that even though fear-related stimuli Illusory Correlation did not differentially predict the occurrence of and Information Processing negative outcomes, they were perceived as if they did. As a consequence, illusory correlation Illusory correlation may also influence how we may maintain or even enhance fear. process emotionally laden stimuli. Tomarken, Mineka, and Cook (1989) were interested in the notion that human fears and phobias are Cognitive Mechanisms associatedwithabiasinhowweprocessinfor- Illusory correlation is a statistical mirage mation, one that confirms and promotes the to which virtually all of us are prone. To maintenance of the fear. Inspired by the work understand why we are susceptible to this of the Chapmans, Tomarken et al. examined cognitive bias, we can think of many events in whetherfearinducescognitivebiasesinthe oureverydaylivesintermsofatableoffour judgment of covariation (association) between probabilities. Using what we term the Great stimuli using an illusory correlation paradigm. Four-fold Table of Life, one can graphically In one experiment, they presented female display the relations between any two events undergraduates,selectedforeitherhighor and nonevents (Lilienfeld et al., 2013). Bor- low levels of snake or spider fears, with a set rowing from the aforementioned lunar lunacy of slides containing fear-relevant (images of example, for instance, we can depict the four ILLUSORY CORRELATION 5 possible probabilities between the full moon fallacy of positive instances and hence illusory and crime: correlation. Theupperleft-handcellofthetable(A) Returningtotheissueofstereotypefor- consists of cases in which both a full moon and mation, one potential explanation for the a crime occurred. The upper right-hand cell emergence of prejudicial beliefs is the fallacy (B) consists of cases in which a full moon, but of positive instances: We may be more likely no crime, occurred. The lower left-hand cell to remember an undesirable behavior when it (C) consists of cases in which there is no full is committed by members of a certain group moon, but a crime occurred. Finally, the lower of people than by others (Feldman, Camburn, right-hand cell (D) consists of cases in which & Gatti, 1986). Once we form an initial belief no full moon and no crime occurred. Research regarding a specific group of people, confir- has shown that we generally overattend to mation bias may predispose us to seek out the upper left-hand (A) cell (Gilovich, 1991), supporting evidence. Furthermore, Hamilton leading us to experience an illusory correla- (1976) showed that stereotyping of minor- tion. Because instances when both a full moon ity groups may result in overestimating the number of times that the associated behavior and a crime occur tend to be memorable and occurred. That is, minority group members confirm our expectations, we attend to and may be falsely remembered to have committed recall them more often. This phenomenon is more undesirable behaviors than is objectively called the “fallacy of positive instances,” which warranted. refers to the tendency for individuals to attend To correctly ascertain the relation between to events that fit their hypotheses (“hits”) and two events, four sources of evidence must be ignore events that do not (“misses”). Fueling considered: the number of times both events illusory correlation is the fact that our minds occurred (cell A), the number of times each usually have a difficult time remembering event occurred in the absence of the other (cells nonevents, those instances when events do not B and C), and the number of times each event occur.Thisunevenattentiontothefourcells didnotoccur(cellD).Whenanindividualfails of the table contributes to the formation of to consider all four possibilities, an illusory illusory correlations. correlation may emerge. Research shows that Our undue attention to the upper left-hand individuals misperceive contingencies because cell of the Great Four-fold Table of Life may they are using only a portion of the available stem from confirmation bias. Confirmation information (Smedslund, 1963). Specifically, bias is the tendency of people to favor informa- people tend to estimate the association between tion that confirms their hypotheses and ignore two events largely using information gathered or underweight evidence that disconfirms from cell A, or the number of instances their hypotheses. By leading individuals to in which both events occurred (Arkes & seek out evidence that supports their beliefs, Harkness, 1980; Nisbett & Ross, 1980). Infor- confirmation bias probably contributes to the mation from all four cells of the table is critical

Did a crime occur?

Yes No

Did a full moon occur? Yes (A) Full moon + crime (B) Full moon + no crime No (C) No full moon + crime (D) No full moon + no crime 6 ILLUSORY CORRELATION to ascertaining whether two events are statis- to reduce certain cognitive biases, such as tically related; by neglecting to avail ourselves hindsight bias, by educating participants of information from Cells C and D, we are regarding a given bias and telling them not ignoring the base rates, or probabilities, of both to be influenced by it when making decisions events (Arkes & Harkness, 1983). (Fischoff, 1977; Wood, 1978). This technique Traditionally, scientists have viewed illu- has been largely ineffective, probably because sory correlation as an error in cognition, individuals often have little awareness of blind but some researchers have argued that our spots in their decision making. Nevertheless, ability to recognize patterns in nature is at we are unaware of similar psychoeducational times adaptive—even when such patterns research on illusory correlation. As an alter- are nonexistent (Fiedler, 2000). For example, native, some researchers have attempted to superstitions are generally regarded as mis- reduce the existence and/or magnitude of takes in cognition arising from incorrect illusory correlation by presenting participants cause-and-effect inferences (Wheen, 2004). with a brief tutorial on Bayesian statistics. The Nevertheless, Shermer (2000) argued that overestimation of the relation between two superstitions are the adaptive outcomes of events often occurs because the base rates of “patternicity,” the tendency to detect meaning- the two events are underutilized (Kahneman & ful patterns in meaningless noise (Tinbergen, Tversky, 1973; Nisbett & Borgida, 1975). Arkes 1963). Shermer noted that humans are faced (1981) suggested that accuracy in estimation with two types of errors when estimating statis- would improve if individuals attended more tical associations: type I errors (false positives) to the prior odds by pitting the prior odds andtypeIIerrors(falsenegatives).Aslongas and the likelihood ratio against each other. the cost of type II errors is sufficiently high, By doing so, an individual cannot ignore the natural selection will favor strategies that result base rates of the two events, which allows the in type I errors because they tend to be less individual to process information from all four dangerous than type II errors (“better safe than cells of the table. Nevertheless, this technique sorry”). For example, all things being equal, it has not yet been put to an experimental test. ismoreprudenttoassumethatabrown,cylin- Relatedly, Matute, Yarritu, and Vadillo (2011) drical object thrashing about in the forest is a found that illusory correlations can be reduced poisonous snake than a fallen tree branch being if individuals understand the conditions in blown by the wind. Using evolutionary mod- which they tend to err in misperceiving the eling, Foster and Kokko (2009) developed a relation between events. Nevertheless, further framework to examine under what conditions work to minimize the likelihood and extent of natural selection would prefer type I errors illusory correlation is clearly necessary. over type II errors. Their model posits that In sum, illusory correlation is a phenomenon natural selection favors strategies that lead to that gives rise to a host of erroneous beliefs incorrect assumptions as long as the occasional in clinical psychology, including the validity correct assumption carries a large fitness bene- of largely unsupported assessment techniques fit (i.e., an increased chance of transmitting the and spurious causes of psychopathology. One organism’s genes to subsequent generations). important area for further work will be to Overall, they concluded that behaviors that are find means of debiasing individuals, including superstitious are virtually inevitable features of mental health professionals, to diminish their adaptive behavior. risk of this important cognitive error.

Debiasing Techniques SEE ALSO: Errors/Biases in Clinical Decision Mak- ing; Meehl, Paul E. (1920–2003); Minnesota Multi- Efforts to attenuate illusory correlation are phasic Personality Inventory (MMPI) Instruments; in their infancy. Researchers have attempted Psychometric Validity; Rorschach Inkblot Test ILLUSORY CORRELATION 7

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