Imagine yourself participating in a pioneering study of how people associate events. Psychologists William Ward and Herbert Jenkins show you the results of a hypothetical fifty-day cloud seeding experiment. They tell you for each day whether clouds were seeded and whether it rained. The information is a random mix: sometimes it rained after seeding, sometimes not. If you believe that cloud seeding works, might you be more likely to notice and recall days with both seeding and rain? In Ward and Jenkins’ experiment, and in many others since, people have become convinced that they really did see precisely what they expected. An overstated Chinese proverb has the idea: ‘‘Two-thirds of what we see is behind our eyes.’’
‘‘Illusory correlations’’—perceiving relationships where none exist —help explain many a superstition, such as the presumption that more babies are born when the moon is full or that infertile couples who adopt become more likely to conceive. Salient coincidences, such as those who conceive after adopting, capture our attention. We focus on them and are less likely to notice what’s equally relevant to assessing correlation—those who adopt and never conceive, those who conceive
without adopting, and those who neither adopt nor conceive. Only when given all this information can we discern whether parents who adopt have elevated conception rates.
Such illusory intuitions help explain why for so many years people believed (as many still do) that sugar made children hyperactive, that cell phones cause brain cancer, that getting cold and wet caused colds, and that weather changes trigger arthritis pain. Physician Don- ald Redelmeier, working with Amos Tversky, followed eighteen ar- thritis patients for fifteen months. The researchers recorded their subjects’ pain reports, as well as each day’s temperature, humidity, and barometric pressure. Despite patients’ beliefs, the weather was uncorrelated with their discomfort, either on the same day or up to two days earlier or later. Shown columns of random numbers labeled ‘‘arthritis pain’’ and ‘‘barometric pressure,’’ even college students saw an illusory correlation. We are, it seems, eager to detect patterns, even when they’re not there.
Likewise, stories of positive-thinking people experiencing cancer remission impress those who believe that positive attitudes counter cancer. Emotions do, we now know, influence health. Mind and body are an integrated system. But to assess whether positive attitudes help defeat cancer we need four bits of information. We need to know how many positive and not-positive thinkers were and were not cured. Without all the data, positive examples tell us nothing about the actual attitudes-cancer correlation.
Shortly after I wrote this, a journalist called, seeking help with a story on why so many famous people (Bill Clinton, Hillary Clinton, Jimmy Carter) have embarrassing brothers. Do they? I responded. Or is our attention just drawn to the salient conjunctions of famous people and boorish brothers? Is boorishness less frequent among men with unfamous siblings, or just less memorable? If we easily deceive ourselves by intuitively seeing what is not there, the remedy is simple: Show me the evidence. Gather and present the comparison data.
Illusory correlations can also fuel misleading stereotypes. Stereo- types assume a correlation between group membership and individ- uals’ characteristics (‘‘Italians are emotional,’’ ‘‘Jews are shrewd,’’ ‘‘Ac- countants are perfectionists’’). Even under the best of conditions, our attentiveness to unusual occurrences can lead our intuition astray.-
Because we are sensitive to distinctive events, the co-occurrence of two distinctive events is especially noticeable. Thus Rupert Brown and Amanda Smith found that British faculty members overestimated the number of (relatively rare, though noticeable) female senior faculty at their university.
David Hamilton and Robert Gifford demonstrated illusory correla- tion in a classic experiment. They showed students slides on which various people, members of Group A or Group B, were said to have done something desirable or undesirable. For example, ‘‘John, a member of Group A, visited a sick friend in the hospital.’’ Twice as many statements described members of Group A as Group B, but both groups did nine desirable acts for every four undesirable behaviors. Since both Group B and the undesirable acts were less frequent, their co-occurrence—for example, ‘‘Allen, a member of Group B, dented the fender of a parked car and didn’t leave his name’’—was an un- usual combination that caught people’s attention. The students therefore overestimated the frequency with which the ‘‘minority’’ group (B) acted undesirably and judged Group B more harshly.
Remember, Group B members actually committed undesirable acts in the same proportion as Group A members. Moreover, the students had no preexisting biases for or against Group B, and they received the information more systematically than daily experience ever offers it. Although researchers debate why it happens, they agree that illusory correlation helps fuel racial stereotypes.
The mass media reflect and feed this phenomenon. When former mental patients like Mark Chapman and John Hinckley, Jr., shoot John Lennon and President Reagan, respectively, the person’s mental history commands attention. Assassins and mental hospitalization are both relatively infrequent, making the combination especially newsworthy. Such reporting adds to the illusory intuition of a large correlation between violent tendencies and mental hospitalization.