PERSONALITY

"Personality" is a broad term that refers to a person's characteristic behaviors, actions, emotions, and thoughts. It is the distinctive way one approaches the world, as manifested in the typical actions, feelings, and cognitions that distinguish one person from another. Historically, scholars have conceptualized personality in three main ways: the trait, cognitive-behavioral, and psychodynamic approaches.

Approaches to personality

The trait approach focuses on relatively enduring dispositions that reside within a person. Traits are almost always defined as dimensions on which every person can be compared with other people. Examples include extroversion, neuroticism, and conscientiousness. This dimensional outlook has historically put a premium on high-quality measurement of traits among those who favor the trait approach, giving that approach a strong quantitative and psychometric flavor. The trait position has also put conceptual and empirical emphasis on demonstrating the stability of these dimensions over situations and time, thus buttressing the fundamental notion that they are long-lasting, internal dispositions that people bring to the situations and contexts they encounter through life.

By contrast, the cognitive-behavioral approach historically has focused on contextual, environmental, and situational determinants of behavior, thought, and feeling, deemphasizing within-person dispositions in favor of external explanations. Advocates of this approach have developed within-person constructs to explain behavior (e.g., self-efficacy, self-concept, mastery, coping strategies), but these are usually framed as variables that arise from experience, and generally involve interaction with the external environment, thus preserving the fundamental viewpoint that external factors are key in understanding personality.

The third major outlook is the psychodynamic approach. It derives from the psychoanalytic theories of Sigmund Freud and his followers, and emphasizes unconscious mental processes as its cardinal theme. This particular approach to personality is aligned more closely with clinical psychology than are the other two positions. Examples of variables that come out of this approach include defense mechanisms and unconscious motives. Together, the trait, cognitive-behavioral, and psychodynamic approaches represent the strongest influences on personality, although others have emerged in recent years, most notably the evolutionary and cross-cultural approaches.

Measurement of personality

Regardless of which approach to personality is adopted, the most widely used method of measurement is self-report. (Other methods include life ratings, observer ratings, and objective tests). Most self-report personality instruments typically use questions or items. Usually these items have been subjected to psychometric analyses, and have been shown to have adequate reliability and validity. Self-report instruments for measuring various personality characteristics abound, although some are used more widely than others.

Some have criticized the reliance on self-report measures by those who study personality and personality development. Such critics argue that more objective means are necessary for the accurate assessment of personality. The chief alternative to self-report is other-report. This broad category includes reports or ratings by peers, spouses, friends, siblings, or trained observers. In other-reports, a subjective judgment is still rendered, but it is deemed more objective in some ways than self-reports, which can be biased by a person's unwillingness to admit faults or weaknesses. Spouse reports or friend reports also are subject to such biases, which makes observer reports attractive to many researchers. Observer reports are usually obtained by associates of the researcher who have been trained to evaluate particular behaviors or actions of the subjects under study, and to code them according to a predetermined scheme. Often, observer reports make use of videotaped behaviors.

Although most personality researchers use self- or other-reports of various kinds, an increasing number are making use of physiological, neurological, and other biological measurements. Assessments of heart rate, blood pressure, neurochemicals (dopamine, epinephrine), and immune system biomarkers (interleukin-1, interleukin-6) are being used by personality researchers with increasing frequency. Neuroimaging techniques have been utilized in a small number of studies of personality. Use of these measurement techniques is not surprising, given the evidence that many aspects of personality have a biological or genetic basis.

Personality stability and change

Together, the three main approaches to personality (trait, cognitive-behavioral, and psychodynamic) have given rise to wide-ranging definitions of personality, spurring confusion regarding the stability of personality over time. Some aspects of personality, such as traits, have been conceptualized as relatively stable over time. Other aspects have been described as malleable and changeable over the life span, including many cognitive-behavioral concepts, such as self-efficacy. To give structure to the issue of personality stability and change, especially in adulthood, Dan P. McAdams has proposed a three-tier model that separates the elements of personality that should remain stable over time from those which are likely to change. This model gained popularity during the 1990s, and by 2001 was a widely cited framework for understanding personality stability and change.

The first tier of the model is comprised of traits, which are defined as relatively enduring patterns of behavior and feelings. In the 1980s and 1990s, a trait model emerged that many consider definitive: the five-factor, or Big Five, model. Via the application of factor analysis (a statistical technique) to large pools of trait questionnaire items or descriptive adjectives, many psychologists concluded that the universe of personality traits can be subsumed under five broad dimensions. These five—extraversion, agreeableness, conscientiousness, neuroticism, and openness to experience—generally make up the cornerstone of the first tier of McAdams's model. Variables at this level often have a physiological or genetic basis, and are hypothesized to change little, if at all, over long periods of time in adulthood.

The second tier is comprised of characteristic adaptations. This is a varied category that is made up of many different kinds of psychological constructs which in general are not as stable or biologically based as traits. Like traits, they are dispositions. However, they are more likely to change over comparable periods of time. Characteristic adaptations include such well-known constructs as coping strategies, goal orientations, defense mechanisms, self-efficacy, control beliefs, mastery, and optimism.

The third tier, life narrative, contains broad elements of personality, such as one's life story, autobiographical memory, and sense of identity. This is the level that most people think of when they contemplate their personalities. Few people see themselves in terms of traits or characteristic adaptations, but most think of their identities or their personal histories when asked to reflect on their personalities. The life narrative tier is hypothesized to change the most over time. As people live their lives, they constantly revise their autobiographies. One's sense of identity, which is often continuous over time, can be revised and modified to better fit one's life and experiences. Thus, at this level, personality should show more change over time than the other two levels (although such change has proven more difficult to assess).

This three-tier model is useful because it provides a framework for organizing the many types of personality variables that have been proposed, and because it allows one to think more clearly about which personality variables should be more stable and which should display more change. Traits should change the least, life narrative the most, and characteristic adaptations should fall in between.

However, there has been no research on stability and change at the life narrative level. Studies of characteristic adaptations have mostly examined stabilities over short periods (a year or less), mainly to establish test-retest reliability. Few studies have considered characteristic adaptations over the long term or have tried to estimate the extent to which they change or are stable.

Traits, on the other hand, have been studied extensively over the long term, with some studies following the same people for 30 years or more. These longitudinal investigations generally focus either on mean-level stability or rank-order stability. The former refers to constancy in the absolute level of a trait over a period of time, as assessed by the arithmetic mean. The latter indexes constancy over time in the relative ordering of people on a trait, and is usually assessed via the correlation coefficient (sometimes adjusted for the reliability of the measure). It gauges the extent to which people retain the same rank within the sample distribution. For example, everyone may decrease over time on a given trait, but if they all decline by roughly the same amount, then the rank ordering of people within the distribution will be preserved, hence giving rise to high rank-order stability. The higher the correlation coefficient between two points in time, the greater the level of preservation of the rank order over that period.

Mean-level stability. The literature focusing on mean-level stability generally has reported change in the Big Five traits over the course of adulthood. The means of extroversion, neuroticism, and openness usually decrease with age. The results with respect to agreeableness and conscientiousness are mixed. It is not clear whether agreeableness changes or not, because some investigations show increases; some, decreases; and others, no change. With regard to conscientiousness, most studies have documented increases, but some studies have shown no change over time.

Rank-order stability. There is a fair amount of consensus with respect to rank-order change. High correlations between measurements of personality on the same people over time means that the relative positions, or ranks, within the sample distribution remain the same. That is, if person A is higher than person B on extroversion at age 30, it is likely that A will still be higher than B at age 60 or 70. Most studies that have followed adults over long periods of time (five to thirty years) have found impressive rank-order constancy. However, these results depend on the length of the longitudinal follow-up period, as a meta-analysis of the literature on the rank-order stability of personality traits concluded (Robertson and Del Vecchio). The correlation coefficients tend to be in the range of .60 to .80 over short periods (less than seven years), but fall to .40 to .60 over longer periods of time (ten years or more). Nonetheless, even over periods of thirty years or more, investigators typically report impressive levels of rank-order constancy. Using extroversion as an example, this implies that a person who is extroverted at age thirty is likely to remain extroverted at ages forty, fifty, sixty, and beyond.

However, the aforementioned meta-analysis concluded that rank-order stability is higher within samples of older adults when compared with samples of midlife or young adults. This would suggest that personality traits become more stable as people grow older. More specifically, relative positions within the distribution appear to become more fixed as older adulthood approaches. Personality traits, therefore, may be more likely to change during youth or middle age than in older adulthood. This does not mean that personality cannot or does not change during older adulthood; it simply means that it is less likely to do so.

Alternative ways of viewing trait stability and change

As valuable as they are, mean-level and rank-order methods often conceal the extent of individual differences in personality trait stability. A trait may show constancy in its mean over time and display strong rank-order consistency, but these statistics are based on groups and may mask change that occurs at the level of the person. Even if a correlation is strong between two time points, this does not mean that everyone retains the same rank order position over the time period. Some people may be changing even as others remain the same. This is essentially a question of individual differences in stability and change. Recently, researchers in this area have turned their attention to stability and change as manifested at the person level, and many are supporting the notion of personality stability and change as a phenomenon of individual differences. These investigators have argued that even if the majority of people show stability over time, not everyone does, and it is thus best to think of personality trait stability in an individual differences framework.

The idea of individual differences in stability and change is not a new one, and can be traced back to various conceptual works in life-span developmental theory, especially the writings of Paul B. Baltes and John R. Nesselroade. In particular, they and other life-span developmentalists have championed the concept of individual differences in intra-individual change. That concept combines the ideas of variability among people (individual differences) and of change that occurs within persons (intra-individual change). The latter requires the estimation of within-person change or stability. Historically, this has been difficult to study, hampered by a lack of adequate statistical techniques. However, beginning in the 1980s, such methods were developed, and by 2000 there were several approaches available to the researcher who wished to assess and analyze within-person change longitudinally.

These techniques are variously known as growth-curve modeling or random effects modeling, among other names. At their most effective, these models require that people be measured at a minimum of three time points, which allows the calculation of growth curves for each individual. The revolutionary aspect of these approaches is that the notion of individual growth curves allows conceptualization of a given trait within a given person as a personality trajectory. Previous research on personality stability and change (whether focusing on rank-order or mean level stability) typically considered only two time points (which allows calculation of only linear trajectories), yielding an impoverished representation of the possible complexity of individual differences in personality change. By the late 1990s, these shortcomings were apparent, and scholars in this area were turning their attention to the various models that allow estimation of trajectories.

The concept of the individual trajectory possesses theoretical relevance because it is the foundational metaphor of the developmental perspective. Before the advent of methods that allowed the estimation of individual trajectories, the basic building block of developmental research, including aging research, was the difference score. Difference scores are obtained by subtracting the score at one time from the score at another. However, difference scores are inherently limited as the basis for developmental analysis, and with techniques now available for modeling multiple occasions of measurement, the trajectory is replacing the difference score.

In addition, the notion of the trajectory allows scholars to link the idiographic and nomothetic traditions in the social sciences. The idiographic approach focuses on information about individual people to better understand unique persons, while the nomothetic position prefers data derived from samples of people in order to discover general laws. The tension between the two is partially resolved by the concept of the trajectory. Trajectories, such as growth curves, can be estimated for large samples but also can be calculated for individuals, allowing for both idiographic and nomothetic analyses of data. Some have argued that the ideal personality theories are those which are broadly applicable to all persons, yet can still be used to explain the behavior of any single person, in essence integrating the idiographic and nomothetic approaches. The trajectory model may prove to be such an integrating force in the area of personality and personality development in the future.

By the late 1990s, investigators had begun applying trajectories techniques to longitudinal personality data. Trajectories can be studied in the aggregate (e.g., the overall trajectory for a sample), but are most interesting when applied to the study of multiple individuals, to permit an analysis of variation among people in trajectories. The key focus, as noted by Baltes and Nesselroade, is the question of interindividual differences in intra-individual change. Persons can differ on trait trajectories in the average level (how much of the trait a person has), the rate of change, and the direction of change. In a small number of studies, investigators have shown that there are significant differences in trajectories among individuals with respect to a number of personality dimensions, including traits. Some people have trait trajectories that rise; some, that fall; and some, that stay stable. Investigators have even found evidence of significant variability in trajectories among older adults. Thus, even as the rank-order stability of personality traits becomes higher among older adults, studies have shown that the ability to change remains. Even if the majority of people remain the same, or at least retain the same relative position within the distribution, it appears that many people do not. Trajectory modeling thus has shed valuable light on the issue of personality trait stability and change. Some people remain stable; others change. Investigators in this area have begun to search for the reasons why some people change and others remain stable.

Daniel K. Mroczek Avron Spiro, III

See also Developmental Psychology.

BIBLIOGRAPHY

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Baltes, P. B.; Reese, H. W.; and NesselRoade, J. R. Life Span Developmental Psychology: Introduction to Research Methods. Monterey, Calif.: Brooks Cole, 1977.

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Lamiell, J. T. "Individuals and the Differences Between Them." In Handbook of Personality. Edited by R. Hogan, J. A. Johnson, and S. R. Briggs. San Diego: Academic Press, 1997. Pages 120–150.

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Roberts, B. W., and Del Vecchio, W. F. "The Rank Order Consistency of Personality Traits from Childhood to Old Age: A Quantitative Review of Longitudinal Studies." Psychological Bulletin 126 (2000): 3–25.