Extraversion and introversion
The trait of extraversion–introversion is a central dimension of human personality theories. The terms introversion and extraversion were first popularized by Carl Jung, although both the popular understanding and psychological usage differ from his original intent. Extraversion tends to be manifested in outgoing, talkative, energetic behavior, whereas introversion is manifested in more reserved, and solitary behavior. Virtually all comprehensive models of personality include these concepts in various forms. Examples include the Big Five model, Jung's analytical psychology, Hans Eysenck's three-factor model, Raymond Cattell's 16 personality factors, the Minnesota Multiphasic Personality Inventory, and the Myers Briggs Type Indicator.
Extraversion and introversion are typically viewed as a single continuum. Thus, to be high on one it is necessary to be low on the other. Carl Jung and the authors of the Myers–Briggs provide a different perspective and suggest that everyone has both an extroverted side and an introverted side, with one being more dominant than the other. Rather than focusing on interpersonal behavior, however, Jung defined introversion as an "attitude-type characterised by orientation in life through subjective psychic contents" (focus on one's inner psychic activity); and extraversion as "an attitude type characterised by concentration of interest on the external object", (the outside world).
In any case, people fluctuate in their behavior all the time, and even extreme introverts and extroverts do not always act according to their type.
Extraversion is "the act, state, or habit of being predominantly concerned with and obtaining gratification from what is outside the self". Extroverts tend to enjoy human interactions and to be enthusiastic, talkative, assertive, and gregarious. They take pleasure in activities that involve large social gatherings, such as parties, community activities, public demonstrations, and business or political groups. Politics, teaching, sales, managing and brokering are fields that favor extroversion. An extroverted person is likely to enjoy time spent with people and find less reward in time spent alone. They tend to be energized when around other people, and they are more prone to boredom when they are by themselves.
Introversion is "the state of or tendency toward being wholly or predominantly concerned with and interested in one's own mental life". Some popular writers have characterized introverts as people whose energy tends to expand through reflection and dwindle during interaction. This is similar to Jung's view, although he focused on psychic energy rather than physical energy. Few modern conceptions make this distinction.
The common modern perception is that introverts tend to be more reserved and less outspoken in groups. They often take pleasure in solitary activities such as reading, writing, using computers, hiking and fishing. The archetypal artist, writer, sculptor, engineer, composer and inventor are all highly introverted. An introvert is likely to enjoy time spent alone and find less reward in time spent with large groups of people, though he or she may enjoy interactions with close friends. Trust is usually an issue of significance: a virtue of utmost importance to an introvert is choosing a worthy companion. They prefer to concentrate on a single activity at a time and like to observe situations before they participate, especially observed in developing children and adolescents. They are more analytical before speaking. Introverts are easily overwhelmed by too much stimulation from social gatherings and engagement, introversion having even been defined by some in terms of a preference for a quiet, more minimally stimulating environment.
Introversion is not seen as being identical to shy or to being a social outcast. Introverts prefer solitary activities over social ones, whereas shy people (who may be extroverts at heart) avoid social encounters out of fear.
Although many people view being introverted or extroverted as a question with only two possible answers, most contemporary trait theories measure levels of extraversion-introversion as part of a single, continuous dimension of personality, with some scores near one end, and others near the half-way mark, see the Big Five personality traits. Ambiversion is falling more or less directly in the middle. An ambivert is moderately comfortable with groups and social interaction, but also can enjoy time alone, away from a crowd.
Extent of extraversion and introversion is most commonly assessed through self-report measures, although peer-reports and third-party observation can also be used. Self-report measures are either lexical  or based on statements. Which measure of either type is used is determined by an assessment of psychometric properties and the time and space constraints of the research being undertaken.
Lexical measures use individual adjectives that reflect extrovert and introvert traits, such as outgoing, talkative, reserved and quiet. Words representing introversion are reverse coded to create composite measures of extraversion/introversion running on a continuum. Goldberg (1992) developed a 20-word measure as part of his 100-word Big Five markers. Saucier (1994) developed a briefer 8-word measure as part of his 40-word mini-markers. However, the psychometric properties of Saucier’s original mini-markers have been found suboptimal with samples outside of North America. As a result, a systematically revised measure was developed to have superior psychometric properties, the International English Mini-Markers. The International English Mini-Markers has good internal consistency reliabilities and other validity for assessing extraversion/introversion and other five factor personality dimensions, both within and, especially, without American populations. Internal consistency reliability of the Extraversion measure for native English-speakers is reported as .92, that for non-native English-speakers is .85.
Statement measures tend to comprise more words, and hence consume more research instrument space, than lexical measures. Respondents are asked the extent to which they, for example, Talk to a lot of different people at parties or Often feel uncomfortable around others. While some statement-based measures of extraversion/introversion have similarly acceptable psychometric properties in North American populations to lexical measures, their generally emic development makes them less suited to use in other populations. For example, statements asking about talkativeness in parties are hard to answer meaningfully by those who do not attend parties, as Americans are assumed to do. Moreover, the sometimes colloquial North American language of statements makes them less suited to use outside America. For instance, statements like Keep in the background and Know how to captivate people are sometimes hard for non-native English-speakers to understand except in a literal sense.
Eysenck's theory 
Hans Eysenck described extraversion-introversion as the degree to which a person is outgoing and interactive with other people. These behavioral differences are presumed to be the result of underlying differences in brain physiology. Extroverts seek excitement and social activity in an effort to heighten their arousal level, whereas introverts tend to avoid social situations in an effort to keep such arousal to a minimum. Eysenck designated extraversion as one of three major traits in his P-E-N model of personality, which also includes psychoticism and neuroticism.
Eysenck originally suggested that extraversion was a combination of two major tendencies, impulsiveness and sociability. He later added several other more specific traits, namely liveliness, activity level, and excitability. These traits are further linked in his personality hierarchy to even more specific habitual responses, such as partying on the weekend.
Eysenck compared this trait to the four temperaments of ancient medicine, with choleric and sanguine temperaments equating to extraversion, and melancholic and phlegmatic temperaments equating to introversion.
Biological factors 
The relative importance of nature versus environment in determining the level of extraversion is controversial and the focus of many studies. Twin studies find a genetic component of 39% to 58%. In terms of the environmental component, the shared family environment appears to be far less important than individual environmental factors that are not shared between siblings.
Eysenck proposed that extraversion was caused by variability in cortical arousal. He hypothesized that introverts are characterized by higher levels of activity than extroverts and so are chronically more cortically aroused than extroverts. The fact that extroverts require more external stimulation than introverts has been interpreted as evidence for this hypothesis. Other evidence of the "stimulation" hypothesis is that introverts salivate more than extroverts in response to a drop of lemon juice.
Extraversion has been linked to higher sensitivity of the mesolimbic dopamine system to potentially rewarding stimuli. This in part explains the high levels of positive affect found in extroverts, since they will more intensely feel the excitement of a potential reward. One consequence of this is that extroverts can more easily learn the contingencies for positive reinforcement, since the reward itself is experienced as greater.
One study found that introverts have more blood flow in the frontal lobes of their brain and the anterior or frontal thalamus, which are areas dealing with internal processing, such as planning and problem solving. Extroverts have more blood flow in the anterior cingulate gyrus, temporal lobes, and posterior thalamus, which are involved in sensory and emotional experience. This study and other research indicates that introversion-extraversion is related to individual differences in brain function.
Extroverts and introverts have a variety of behavioral differences. According to one study, extroverts tend to wear more decorative clothing, whereas introverts prefer practical, comfortable clothes. Extroverts are likely to prefer more upbeat, conventional, and energetic music than introverts. Personality also influences how people arrange their work areas. In general, extroverts decorate their offices more, keep their doors open, keep extra chairs nearby, and are more likely to put dishes of candy on their desks. These are attempts to invite co-workers and encourage interaction. Introverts, in contrast, decorate less and tend to arrange their workspace to discourage social interaction.
Humans are complex and unique, and because introversion-extraversion varies along a continuum, individuals may have a mixture of both orientations. A person who acts introverted in one scenario may act extroverted in another, and people can learn to act "against type" in certain situations. Jung's theory states that when someone's primary function is extroverted, his secondary function is always introverted (and vice versa).
Acknowledging that introversion and extraversion are normal variants of behavior can help in self-acceptance and understanding of others. For example, an extrovert can accept her introverted partner's need for space, while an introvert can acknowledge his extroverted partner's need for social interaction.
Researchers have found a correlation between extraversion and happiness. That is, more extroverted people tend to report higher levels of happiness than introverts. Other research has shown that being instructed to act in an extroverted manner leads to increases in positive affect, even for people who are trait-level introverts.
This does not mean that introverts are unhappy. Extroverts simply report experiencing more positive emotions, whereas introverts tend to be closer to neutral. This may be due to the fact that extraversion is socially preferable in Western culture and thus introverts feel less desirable. In addition to the research on happiness, other studies have found that extroverts tend to report higher levels of self-esteem than introverts. Others suggest that such results reflect socio-cultural bias in the survey itself.[dead link] Dr. David Meyers has claimed that happiness is a matter of possessing three traits: self-esteem, optimism, and extraversion. Meyers bases his conclusions on studies that report extroverts to be happier; these findings have been questioned in light of the fact that the "happiness" prompts given to the studies' subjects, such as "I like to be with others" and "I'm fun to be with," only measure happiness among extroverts. Also, according to Carl Jung, introverts acknowledge more readily their psychological needs and problems, whereas extroverts tend to be oblivious to them because they focus more on the outer world.
Extraversion is perceived as socially desirable in Western culture, but it is not always an advantage. For example, extroverted youths are more likely to engage in delinquent behavior. Conversely, while introversion is perceived as less socially desirable, it is strongly associated with positive traits such as intelligence and "giftedness." For many years, researchers have found that introverts tend to be more successful in academic environments, which extroverts may find boring. Career counselors often use personality traits, along with other factors such as skill and interest, to advise their clients. Some careers such as computer programming may be more satisfying for an introverted temperament, while other areas such as sales may be more agreeable to the extroverted type.
Although neither introversion nor extraversion is pathological, psychotherapists can take temperament into account when treating clients. Clients may respond better to different types of treatment depending on where they fall on the introversion/extraversion spectrum. Teachers can also consider temperament when dealing with their pupils, for example acknowledging that introverted children need more encouragement to speak in class while extroverted children may grow restless during long periods of quiet study.
Regional variation 
||The examples and perspective in this section deal primarily with the U.S and do not represent a worldwide view of the subject. (January 2012)|
Some claim that Americans live in an "extroverted society" that rewards extrovert behavior and rejects introversion. This is because the US is currently a culture of personality, whereas other cultures are cultures of character where people are valued for their "inner selves and their moral rectitude". Other cultures, such as Central Europe, Japan or regions where Buddhism, Sufism etc. prevail, prize introversion. These cultural differences predict individuals' happiness such that people who score higher in extraversion are happier, on average, in particularly extroverted cultures and vice versa.
Researchers have found that people who live on islands tend to be less extroverted (more introverted) than those living on the mainland, and that people whose ancestors had inhabited the island for twenty generations tend to be less extroverted than more recent arrivals. Furthermore, people who emigrate from islands to the mainland tend to be more extroverted than people that stay on islands, and those that immigrate to islands.
In the United States, researchers have found that people living in the midwestern states of North Dakota, South Dakota, Nebraska, Minnesota, Wisconsin, and Illinois score higher than the U.S. average on extraversion. Utah and the southeastern states of Florida and Georgia also score high on this personality trait. The most introverted states in the United States are Maryland, New Hampshire, Alaska, Washington, Oregon and Vermont. People who live in the northwestern states of Idaho, Montana, and Wyoming are also relatively introverted.
Extraversion, introversion, and happiness 
||It has been suggested that Personality# Extraversion and happiness be merged into this article. (Discuss) Proposed since December 2012.|
Extroverts are found to have higher levels of happiness and positive affect than introverts. An influential review article concluded that personality, specifically extraversion and emotional stability, was the best predictor of subjective well-being. As examples, Argyle and Lu (1990) found that the trait of extraversion, as measured by Extraversion Scale of the Eysenck Personality Questionnaire (EPQ), was positively and significantly correlated with happiness, as measured by the Oxford Happiness Inventory. Using the same happiness and extraversion scales, Hills and Argyle (2001) found that happiness was again significantly correlated with extraversion. Also, the study by Emmons and Diener (1986) showed that extraversion correlates positively and significantly with positive affect but not with negative affect. Similar results were found in a large longitudinal study by Diener, Sandvik, Pavot, and Fujita (1992), which assessed 14,407 participants from 100 areas of continental United States. Using the abbreviated General Well-Being Schedule, which tapped positive and negative affects, and Costa and McCrae's (1986) short version of the NE0's Extraversion scale, the authors reported that extroverts experienced greater well-being at two points in time, during which data were collected: first between 1971 and 1975, and later between 1981 and 1984. Furthermore, Larsen and Ketelaar (1991) showed that extroverts respond more to positive affect than to negative affect, since they exhibit more positive-affect reactivity to the positive-affect induction, yet they do not react more negatively to the negative-affect induction.
Possible reasons 
Instrumental view 
- Personality trait as a cause of higher sociability
According to the instrumental view, one explanation for greater subjective well-being among extroverts could be the fact that extraversion helps in the creation of life circumstances, which promote high levels of positive affect. Specifically, the personality trait of extraversion is seen as a facilitator of more social interactions, since the low cortical arousal among extroverts results in them seeking more social situations in order to increase their arousal.
- The social participation theory
According to the social participation theory, more frequent participation in social situations creates more frequent, and higher levels, of positive affect. Therefore, it is believed that since extroverts are characterized as more sociable than introverts, they also possess higher levels of positive affect brought on by social interactions. Specifically, the results of Furnham and Brewin's study (1990) suggest that extroverts enjoy and participate more in social activities than introverts, and as a result extroverts report higher level of happiness. Also, in the study of Argyle and Lu (1990) extroverts were found to be less likely to avoid participation in noisy social activities, and to be more likely to participate in social activities such as: party games, jokes, or going to the cinema. Similar results were reported by Diener, Larsen, and Emmons (1984) who found that extroverts seek social situations more often than introverts, especially when engaging in recreational activities.
However, a variety of findings contradict the claims of the social participation theory. Firstly, it was found that extroverts were happier than introverts even when alone. Specifically, extroverts tend to be happier regardless of whether they live alone or with others, or whether they live in a vibrant city or quiet rural environment. Similarly, a study by Diener, Sandvik, Pavot, and Fujita (1992) showed that although extroverts chose social jobs relatively more frequently (51%) than nonsocial jobs compared to introverts (38%), they were happier than introverts regardless of whether their occupations had social or nonsocial character. Secondly, it was found that extroverts only sometimes reported greater amounts of social activity than introverts, but in general extroverts and introverts do not differ in the quantity of their socialization. Similar finding was reported by Srivastava, Angelo, and Vallereux (2008), who found that extroverts and introverts both enjoy participating in social interactions, but extroverts participate socially more. Thirdly, studies have shown that both extroverts and introverts participate in social relations, but that the quality of this participation differs. The more frequent social participation among extroverts could be explained by the fact that extroverts know more people, but those people are not necessarily their close friends, while introverts, when participating in social interactions, are more selective and have only few close friends with whom they have special relationships.
- The social attention theory
Yet another explanation of the high correlation between extraversion and happiness comes from the study by Ashton, Lee, and Paunonen (2002). They suggested that the core element of extraversion is a tendency to behave in ways that attract, hold, and enjoy social attention, and not reward sensitivity. They claimed that one of the fundamental qualities of social attention is its potential of being rewarding. Therefore, if a person shows positive emotions of enthusiasm, energy, and excitement, that person is seen favorably by others and he or she gains others' attention. This favorable reaction from others likely encourages extroverts to engage in further extroverted behavior. Ashton, Lee, and Paunonen's (2002) study showed that their measure of social attention, the Social Attention Scale, was much more highly correlated with extraversion than were measures of reward sensitivity.
Temperamental view 
- The affective reactivity model
The affective reactivity model states that the strength of a person's reactions to affect-relevant events are caused by people's differences in affect. This model is based on the reinforcement sensitivity theory by Jeffrey Alan Gray, which states that people with stronger behavioral activation system (BAS) are high in reward responsiveness and are predisposed to the personality trait of extraversion, while people with a stronger behavioral inhibition system (BIS) are lower in reward responsiveness and are more predisposed to personality trait of neuroticism and introversion. Therefore, extroverts are seen as having a temperamental predisposition to positive affect since positive mood induction has a greater effect on them than on introverts, thus extroverts are more prone to react to pleasant effects. For example, Gable, Reis, and Elliot (2000). found in two consecutive studies that people with more sensitive BIS reported higher levels of average negative affect, while people with more sensitive BAS reported higher levels of positive affect. Also Zelenski and Larsen (1999) found that people with more sensitive BAS reported more positive emotions during the positive mood induction, while people with more sensitive BIS reported more negative emotions during the negative mood induction.
- The social reactivity theory
The social reactivity theory alleges that all humans, whether they like it or not, are required to participate in social situations. Since extroverts prefer engaging in social interactions more than introverts, they also derive more positive affect from such situations than introverts do. The support for this theory comes from work of Brian R. Little, who popularized concept of "restorative niches". Little claimed that life often requires people to participate in social situations, and since acting social is out of character for introverts, it was shown to harm their well-being. Therefore, one way to preserve introverts' well-being is for them to recharge as often as possible in places where they can return to their true selves - places Little calls "restorative niches".
- Affective regulation
Another possible explanation for more happiness among extroverts comes from the fact that extroverts are able to better regulate their affective states. This means that in ambiguous situations (situations where positive and negative moods are introduced and mixed in similar proportions) extroverts show a slower decrease of positive affect, and, as a result, they maintained a more positive affect balance than introverts. Extroverts may also choose activities that facilitate happiness (e.g., recalling pleasant vs. unpleasant memories) more than introverts when anticipating difficult tasks.
- The set-point model aka affect-level model
According to the set-point model, levels of positive and negative affects are more or less fixed within each individual, hence, after a positive or negative event, people's moods tend to go back to the pre-set level. According to the set-point model, extroverts' experience more happiness because their pre-set level of positive affect is set higher than the pre-set point of positive affect in introverts, therefore extroverts require less positive reinforcement in order to feel happy.
- Pleasure-arousal relation
A study by Kuppens (2008) showed that extroverts and introverts engage in different behaviors when feeling pleasant, which could be a potential explanation for underestimating the frequency and intensity of happiness exhibited by introverts. Specifically, Kuppens (2008) found that arousal and pleasantness are positively correlated for extraverts, which means that pleasant feelings are more likely to be accompanied by high arousal for extraverts. On the other hand, arousal and pleasantness are negatively correlated for introverts, resulting in introverts exhibiting low arousal when feeling pleasant. In other words, if everything is going well in an extravert's life, which is a source of pleasant feelings, extroverts see such situation as an opportunity to engage in active behavior and goal pursuit, which brings about an active, aroused pleasant state. Yet, when everything is going good for introverts, they see it as an opportunity to let down their guard, resulting in them feeling relaxed and content.
See also 
- Analytical psychology
- Alternative five model of personality
- Big Five personality traits
- Myers-Briggs Type Indicator
- Reinforcement sensitivity theory
- Trait theory
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- Secrets of a super successful introvert Susan Cain article from CNN Living
- TED talks – Susan Cain: The power of introverts talk by Susan Cain, author of Quiet: The Power of Introverts in a World That Can't Stop Talking (January 2012), talks about reasons we should celebrate and encourage introversion
- Revenge of the Introvert Laurie Helgoe's article about introversion published in Psychology Today (2010)
- General description of the types Jung's original article (1921)
- BBC – The Human Mind – Personality Description of introversion and extraversion, focusing on reward-seeking behavior
- Changing Minds Another description of introversion and extraversion, taking a Jungian view
- Extraversion Gale Encyclopedia of Childhood & Adolescence. Gale Research, 1998.
- Introversion Gale Encyclopedia of Childhood & Adolescence. Gale Research, 1998.
- USA Today article about CEO introverts/extroverts
- Caring for Your Introvert Article in the Atlantic, March 2003
- Ten Myths About Introverts Article by Carl King, 2009.
- J. Wilt and W. Revelle review chapter on extraversion