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Some debates have pervaded the field of psychology since its genesis. Perhaps one of the most salient ones deals with the nature of personality. Personality psychology studies one's distinctive style of cognition, behavior, and affect. However, this concept elicits discord among psychologists as some have insisted that it does not exist, while others struggle with issues of measurement.
Personality, one's characteristic way of feeling, behaving and thinking, is often conceptualized as a person's standing on each Big Five personality trait (extraversion, neuroticism, openness to experience, agreeableness and conscientiousness). A person's personality profile is thus gauged from their standing on five broad concepts which predict, among other life outcomes, behavior and the quality of interpersonal relationships. Initially, it was believed that one's Big Five profile was static and dichotomous in that one was either at one extreme of each trait or another  For example, people are typically categorized as introverted or extraverted. Personality was therefore assessed in terms of generalities or averages. In noticing the strong inconsistencies in how people behaved across situations, some psychologists dismissed personality as nonexistent.
This school of thought attributes human behavior to environmental factors, relegating individual differences to situational artifacts and contesting the existence of individual predispositions. It was led by situationists like Walter Mischel (1968). Their contention held that personality was a fictitious concept. For them, the discrepancies observed across one's behaviors were evidence that interindividual differences did not exist  Some aspects of the situationist perspective even suggest that all human beings are the same and that the differences we observe are simply illusory biproducts of the environment.
However, personologists soon integrated these inconsistencies into their conceptualization of personality. They modified the old, more monolithic construct by measuring how people differ across situations. Their new methods of personality assessment describe fluctuations in personality characteristics as consistent and predictable for each person based on the environment he is in and his predispositions. Some work suggests that people can espouse different levels of a personality dimension as the social situations and time of day change
Therefore, someone is not conscientious all the time, but can be conscientious at work and a lot less so when she is home. This work also suggests that intrapersonal variations on a trait can be even larger than interpersonal variations. Extraversion varies more within a person than across individuals, for example. This work was based on individual self-ratings during the day across a long period of time. This allowed for researchers to assess moment-to-moment and day to day variations on personality attributes. Personologists now tend to agree that people's personalities are variegated and are not to be conceptualized through bipolar characterizations (e.g. extraversion vs introversion). Rather people oscillate between the two extremes of a trait. The pattern of this oscillation then constitutes personality.
In addition, social roles (e.g. employee) have been identified as a potential sources of personality change. Researchers have found strong correspondences between the demands of a social role and one's personality profile. If the role requires that the person enacting it be conscientious, her standing on this trait is more likely to be high. Conversely, once he leaves that role and or takes on another which entails less conscientiousness, he will manifest a lower level standing on that trait. Longitudinal research demonstrates that people's personality trajectories can often be explained by the social roles they espoused and relinquished throughout their life stages. Thus social roles are often studied as fundamental predictors of personality. The goals associated with them elicit the appropriation of certain personality profiles by the people enacting them. For example, employees judged effective by their peers and superiors are often described as conscientious as well.
Personality also changes through life stages. This may be due to physiological changes associated with development but also experiences that impact behavior. Adolescence and young adulthood have been found to be prime periods of personality changes, especially in the domains of extraversion and agreeableness. It has long been believed that personality development is shaped by life experiences that intensify the propensities that led individuals to those experiences in the first place, which is known as the corresponsive principle.
Subsequent research endeavors have integrated these findings in their methods of investigation. Researchers distinguish between mean level and rank order changes in trait standing during old age. Their study of personality trajectories is thus contingent on time and on age considerations. Mottus, Johnson and Geary (2012) found that instability engendered by aging does not necessarily affect one's standing within an age cohort. Hence, fluctuations and stability coexist so that one changes relative to one's former self but not relative to one's peers. Similarly, other psychologists found that Neuroticism, Extraversion (only in men), and Openness decreased with age after 70, but Conscientiousness and Agreeableness increased with age (the latter only in men). Moreover, they suggest that there is a decline on each trait after the age of 81.
Inconsistency as a trait
Personality inconsistency has become such a prevalent consideration for personologists that some even conceptualize it as a predisposition in itself. Fleisher and Woehr (2008) suggest that that consistency across the Big Five is a construct that is fairly stable and contributes to the predictive validity of personality measures. Hence inconsistency is quantifiable much like a trait and constitutes an index of and enhances the fit of psychological models.
To accommodate the inconsistency demonstrated on personality tests, researchers developed the Frame Of Reference principle (FOR). According to this theory, people tend to think of their personality in terms of a specific social context when they are asked to rate them. Whichever environment is cognitively salient at the time of the personality measurement will influence the respondent's ratings on a trait measure. If, for example, the person is thinking in terms of their student identity, then the personality ratings he reports will most likely reflect the profile he espouses in the context of student life. Accounting for the FOR principle aims at increasing the validity of personality measures. This demonstrates that the predictive validity of personality measures which specify a social context is a lot higher than those measures which take a more generic approach.
This point is substantiated by yet another body of work suggesting that FOR instructions moderated the link between extraversion and openness scores on manager ratings of employee performance  This research thus recognizes the importance of intrapersonal fluctuations contingent on personality is context specific and is not necessarily generalizable across social domains and time.
Change over a lifetime
There are two very specific types of change that researchers tend to focus on: rank-order change and mean-level change. A rank-order change refers to a change in an individual's personality trait relative to other individuals; such changes do not occur very often. A mean-level change refers to an absolute change in the individual's level of a certain trait over time. Longitudinal research shows that mean-level change does occur. However, some traits tend to change while some traits tend to stay stable.
There is an increase in consistency of a trait as age increases. However, personality does not stop changing at a specific age. Biological and social transitions in life may also be a factor for change. Biological transitions are stages like puberty or first childbirth. Social transitions might be changes in social roles like becoming a parent or working at a first job. These life transitions do not necessarily cause change, but they may be reasons for change. One theory says that whether or not these life transitions cause personality change is based on whether the transition was expected based on age or was unforeseen. The events that are expected will cause personality change because those events have common scripts. However, events that are unexpected will give prominence to the traits that already exist for the individual. Historical context also affects personality change. Major life events can lead to changes in personality that can persist for more than a decade. A longitudinal study followed women over 30 years and found that they showed increases in individualism. This may have been due to the changes that were occurring in the country at the time.
Stressful life events
Negative life events, long-term difficulties, and deteriorated life quality, all predict small but persistent increases in neuroticism, while positive life events, and improved life quality, predict small but persistent decreases in neuroticism. There appears to be no point during the lifespan that neuroticism is immutable, which is known as the plasticity principle.
Mechanisms of change
There are multiple ways for an individual's personality to change. Individuals will change their behavior based on the ideas in their environment that emit rewards and punishments. Some of these ideas might be implicit, like social roles. The individual changes his or her personality to fit into a social role if it is favorable. Other ideas might be more explicit like a parent trying to change a child's behavior. An individual may decide to actively try to change his or her own behavior/ personality after thinking about his or her own actions. Therapy involves the same type of introspection. The individual along with the therapist identifies the behaviors that are inappropriate, and then self-monitors in order to change them. Eventually the individual internalizes the behavior they want to attain, and that trait will generalize to other areas of the individual's life. Personality change also occurs when individuals observe the actions of others. Individuals may mimic the behaviors of others and then internalize those behaviors. Once the individual internalizes those behaviors they are said to be a part of that person's personality. Individuals also receive feedback from other individuals or groups about their own personality. This is a driving force of change because the individual has social motivations to change his or her personality. It has also been shown that major positive and negative life events can predict changes in personality.
Change in the Big Five
The Big Five personality traits are often used to measure change in personality. There is a mean-level change in the Big Five traits from age 10 to 65. The trends seen in adulthood are different from trends seen in childhood and adolescence. Some research suggests that during adolescence rank-order change does occur and therefore personality is highly unstable. Gender differences are also shown before adulthood. Conscientiousness drops from late childhood to adolescence, but then picks back up from adolescence into adulthood. Agreeableness also drops from late childhood to adolescence, but then picks back up from adolescence into adulthood. Neuroticism shows a different trend for males and females in childhood and adolescence. For females, Neuroticism increases from childhood to adolescence. Then Neuroticism levels from adolescence into adulthood and continues the adult trend of decreasing. Males however, tend to gradually decrease in Neuroticism from childhood to adolescence into adulthood. Extraversion drops from childhood to adolescence and then does not really change that much. Openness to experience also shows a different trend for different genders. Females tend to decrease in Openness to experience from childhood to early adulthood and then gradually increases all throughout adulthood. Males tend to decrease in Openness to experience from childhood to adolescence, then it tends to increase through adulthood. In adulthood, Neuroticism tends to decrease, while Conscientiousness and Agreeableness tend to increase. Extraversion and Openness to experience do not seem to change much during adulthood. These trends seen in adulthood are different from trends seen in childhood and adolescence. Cross-cultural research shows that German, British, Czech, and Turkish people show similar trends of these personality traits.
The Big Five personality traits can also be broken down into facets. Different facets of each personality trait are often correlated with different behavioral outcomes. Breaking down the personality traits into facets is difficult and not yet at a consensus. However, it is important to look at change in facets over a lifetime separate from just the change in traits because different facets of the same trait show different trends. Neuroticism can be broken into the two facets of anxiety and depression. Anxiety has the same trend as Neuroticism for both males and females. For females, anxiety increases from childhood to adolescence, at emerging adulthood it levels out, and then starts to decrease into and throughout middle age. Anxiety in males tends to decrease from late childhood through adulthood. Depression (not clinical depression, but rather susceptibility to negative affect) shows two peaks in females. Females tend to have higher levels of this kind of depression in adolescence and then again in early adulthood. Depression does, however, have a negative trend through adulthood. For males, depression tends to show an increase from childhood to early adulthood and then shows a slight decrease through middle age.
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