Individual Differences Definition
Individual differences are the more-or-less enduring psychological characteristics that distinguish one person from another and thus help to define each person’s individuality. Among the most important kinds of individual differences are intelligence, personality traits, and values. The study of individual differences is called differential or trait psychology and is more commonly the concern of personality psychologists than social psychologists. Individual differences are neither a fiction nor a nuisance; they are enduring psychological features that contribute to the shaping of behavior and to each individual’s sense of self. Both social and applied psychology can benefit by taking these enduring dispositions into account.
Background and History
Individual differences in cognitive abilities have been studied since the 19th century, when Sir Francis Galton published Hereditary Genius, and they have continued to occupy the attention of psychologists, including Alfred Binet and David Wechsler, who produced some of the most widely used measures of intelligence. Individual differences in personality traits were studied conceptually by Gordon Allport and more empirically by Raymond Cattell and Hans Eysenck. Current views on individual differences in personality are dominated by the Five-Factor Model or Big Five.
Most individual differences are a matter of degree. Although it is convenient to talk about introverts and extraverts as if these were two distinct classes of people, in fact most people have some features of both introversion and extraversion and would fall near the middle of the distribution. Most traits are distributed in the familiar bell-shaped curve; there is little evidence for distinct types in psychology.
At any given time, people differ in their moods and their opinions of the weather. But the individual differences of greatest interest are those that reflect some enduring aspect of the individual. Both cognitive and personality traits meet this description. Longitudinal studies conducted over periods as long as several decades show that in adults, traits like verbal intelligence, emotional stability, and musical ability are exceptionally stable, with very gradual changes and high rank-order consistency. Young adults who are bright, unflappable, and tone-deaf are likely to be bright, unflappable, and tone-deaf 40 years later.
Several explanations have been offered for the stability of traits. For example, it is sometimes said that people build a life-structure that sustains their traits. The intellectually curious woman subscribes to magazines that continue to stimulate her curiosity and exercise her intellect. The sociable man acquires a circle of friends who reinforce his sociability. In addition, however, there is now compelling evidence from hundreds of studies that both cognitive and personality traits are substantially heritable, and the same genes that make one, say, suspicious at age 30 make one suspicious at age 70.
Ralph Waldo Emerson, the American transcendental philosopher, was dismayed by the evidence of trait consistency he saw, because it seemed to him to deprive people of freedom of will: “Temperament,” he wrote, “puts all divinity to rout.” But people generally embrace their own traits, recognizing them as integral parts of their identity. People might sometimes wish to be more assertive, organized, or imaginative, but in the long run, most accept their traits as their own authentic selves.
The consistency of traits over time is not matched by their consistency over situations. Sometimes friendly people smile at strangers; sometimes they don’t. They may be preoccupied by an upcoming interview or depressed by the morning’s news. When, in the 1960s, psychologists began to document this inconsistency in laboratory studies of behavior, it ignited one of the most celebrated controversies in the history of psychology, the person-situation debate. Some researchers were so struck by inconsistency that they came to believe that traits were completely fictional, that is, stories people made up about themselves or adopted from others. The consistency of traits over time was, these skeptics thought, merely the stability of a myth.
Eventually a more sophisticated understanding of traits emerged. Traits are only one of many influences on behavior at any particular time, so consistency between one situation and another is quite limited. But traits are enduring, so over a period of days or months, they have a cumulative effect on the pattern of behavior that we recognize as sociability or nervousness or stubbornness, and it is this general pattern that is stable over time. In gambling casinos, the house sometimes wins, sometimes loses—but in the long run, owning a casino is almost guaranteed to make you rich. Traits operate in the same probabilistic way.
Individual Differences and Social Psychology
Curiously, individual differences first came to the attention of experimentalists as a source of consistent error. In the 19th century, astronomy depended on human recordings of the precise moment when an object crossed a specified point in the sky, and different astronomers reported slightly different values. Charles Wolf noted that these discrepancies were consistent, and he developed personal equations to correct the reports of different observers. Studies of perceptual speed and reaction time grew out of this observation.
For some social psychologists, individual differences are nuisance variables that make life more difficult. In the typical social psychology experiment, subjects are randomly assigned to different conditions and exposed to different experimental manipulations; their behavior is then recorded. In this way, the experimenter hopes to learn how people respond to different situations. For example, terror management theory suggests the hypothesis that people should become more patriotic when reminded of death. So subjects might be shown scenes either of a cemetery or a parking lot and then be asked their evaluation of the national flag. One would expect a range of responses, but if the theory is right and the experiment well done, then on average those individuals who saw the cemetery should report more positive feelings about the flag.
But there are also enduring individual differences in patriotism, and those are likely to cloud the results. By randomly assigning subjects to conditions, one hopes to equalize the effects of individual differences, but they still contribute noise. In principle, one could assess patriotism separately (perhaps a month before the experiment) and remove its effects statistically. In practice, this is rarely done.
Other social psychologists, however, realize that individual differences can be utilized as a natural experiment. Arie Kruglanski and colleagues proposed that decisions are often made on the basis of a need for closure—the need to reach a definite conclusion (regardless of its correctness). Experimentally, this need can be manipulated by varying time pressure on subjects or even by making the task unpleasant by conducting the study in the same room as a noisy computer printer. Under these conditions, people tend to seize on the first information they are given and freeze their opinions. But Kruglanski also realized that there may be individual differences in the need for closure (in fact, related to the personality trait of low Openness to Experience) and that individuals who are high in need for closure may habitually react like people put under time pressure. A series of experiments confirmed this hypothesis.
Individual differences may also interact with experimental manipulations. The sight of a cemetery may be a much more powerful cue to death for someone chronically high in anxiety and thus may have a correspondingly stronger effect on subsequent patriotism. A stubborn and antagonistic subject may resent the experimenter’s attempted time pressure manipulations and deliberately ignore them. Social psychologists routinely examine their data to see if the effects are different for men and women; perhaps they should routinely assess traits and their interactions with manipulations.
Most of the topics of interest to social psychologists, including attachment, achievement motivation, risk-taking, prejudice, altruism, and self-regulation, are associated with enduring individual differences. Social psychologists usually study the mechanisms by which these phenomena operate or the conditions that enhance or reduce them. By understanding the processes that give rise to behavior, social psychologists hope to be able to develop interventions to change them. Individual differences are, by and large, not easily altered, so they sometimes seem irrelevant to interventionists.
But it makes sense to consider trait levels in attempting to change behavior. For example, researchers may wish to help dieters control their eating behavior. Researchers know that people high in Conscientiousness are more self-disciplined than those low in Conscientiousness, and this information can figure into the approach to the problem. For conscientious dieters, researchers might need only to focus on education: If they understand the principles of nutrition and the health risks of obesity, they may have enough incentive to change their eating habits. Dieters low in Conscientiousness need more help; extra encouragement, group support, or a locked refrigerator may be required. Other individual differences might also be relevant to the selection of treatments. Some people eat less when alone or when eating with other people who are also dieting. Assigning introverts to the former condition and extraverts to the latter might facilitate self-control in a congenial setting.
References:
- Carver, C. S. (2005). Impulse and constraint: Perspectives from personality psychology, convergence with theory in other areas, and potential for integration. Personality and Social Psychology Review, 9, 312-333.
- Costa, P. T., Jr., & McCrae, R. R. (1998). Trait theories of personality. In D. F. Barone, M. Hersen, & V. B. V. Hasselt (Eds.), Advanced personality (pp. 103-121). New York: Plenum.
- Kruglanski, A. W., & Webster, D. M. (1996). Motivated closing of the mind: “Seizing” and “freezing.” Psychological Review, 103, 263-283.
- McCrae, R. R., & Costa, P. T., Jr. (2003). Personality in adulthood: A Five-Factor Theory perspective (2nd ed.). New York: Guilford Press.