People love to fit themselves and their friends into “types”; they have been doing it forever. Early Greek philosophers thought our personalities fell into four fundamental categories depending on mixes of body fluids. If you were an angry, irritable sort of person, you supposedly had an excess of choler, and even now the word choleric describes a hothead. And if you were sluggish and unemotional, you supposedly had an excess of phlegm, making you a “phlegmatic” type.

That particular theory is long gone, but unscientific tests of personality types still exist, aimed at predicting how people will do at work, whether they will get along with others, or whether they will succeed as leaders. One such test, the Myers–Briggs Type Indicator, is hugely popular in business, at motivational seminars, and with matchmaking services; at least 2.5 million Americans take it each year (Gladwell, 2004). The test assigns people to one of 16 different types, depending on how an individual scores on the dimensions of introverted or extroverted, logical or intuitive. Unfortunately, the Myers–Briggs test is not much more reliable than measuring body fluids; one study found that fewer than half of the respondents scored as the same type a mere five weeks later. Worse, knowledge of a person's type does not reliably predict that person's behavior on the job or in relationships (Barbuto, 1997; Paul, 2004; Pittenger, 1993, 2005). Equally useless from a scientific point of view are many of the tests used by businesses and government to predict which “types” are apt to steal, take drugs, or be disloyal on the job (Ehrenreich, 2001).

Identifying broad personality “types” hasn't advanced the study of personality much, although the study of specific traits of an individual—habitual ways of behaving, thinking, and feeling—has produced many measures that are scientifically valid and useful in research. These objective tests (inventories) are standardized questionnaires requiring written responses, typically to multiple-choice or true–false items. They provide information about countless aspects of personality, including values, interests, self-esteem, emotional problems, and typical ways of responding to situations. Using well-constructed inventories, psychologists have identified hundreds of traits, ranging from sensation-seeking (the enjoyment of risk) to mood awareness (attention directed toward one's emotional states) to perfectionism (a striving for flawlessness). The hallmarks of a sound psychological test are reviewed in the video Measuring Personality.

Are some personality traits more important or central than others? Do some of them overlap or cluster together? For Gordon Allport, one of the most influential psychologists in the empirical study of personality, the answer to both questions was yes. Allport (1961) recognized that not all traits have equal weight and significance in people's lives. Most of us, he said, have five to ten central traits that reflect a characteristic way of behaving, dealing with others, and reacting to new situations. For instance, some people see the world as a hostile, dangerous place, whereas others see it as a place for fun and frolic. Secondary traits, in contrast, are more changeable aspects of personality, such as music preferences, habits, casual opinions, and the like.

Raymond B. Cattell (1973) advanced the study of this issue by applying a statistical method called factor analysis. Performing a factor analysis is like adding water to flour: It causes the material to clump up into little balls. When applied to traits, this procedure identifies clusters of correlated items that seem to be measuring some common, underlying factor. Today, hundreds of factor-analytic studies support the existence of a cluster of five central “robust factors,” known informally as the Big Five (Chang, Connelly, & Geeza, 2012; Costa & McCrae 2011, 2014; McCrae et al., 2005; Paunonen, 2003; Roberts & Mroczek, 2008):

1. Extroversion versus introversion describes the extent to which people are outgoing or shy. It includes such traits as being sociable or reclusive, adventurous or cautious, socially dominant or more passive, eager to be in the limelight or inclined to stay in the shadows.

2. Neuroticism (negative emotionality) versus emotional stability describes the extent to which a person suffers from such traits as anxiety, an inability to control impulses, and a tendency to feel negative emotions such as anger, guilt, contempt, and resentment. Neurotic individuals are worriers, complainers, and defeatists, even when they have no major problems. They are always ready to see the sour side of life and none of its sweetness (Barlow et al., 2014).

3. Agreeableness versus antagonism describes the extent to which people are good-natured or irritable, cooperative or abrasive, secure or suspicious and jealous. It reflects the tendency to have friendly relationships or hostile ones.

4. Conscientiousness versus impulsiveness describes the degree to which people are responsible or undependable, persevering or quick to give up, steadfast or fickle, tidy or careless, self-disciplined or impulsive.

5. Openness to experience versus resistance to new experience describes the extent to which people are curious, imaginative, questioning, and creative or conforming, unimaginative, predictable, and uncomfortable with novelty.

In spite of some cultural variations, the Big Five have emerged as central personality dimensions throughout the world, in countries as diverse as Britain, Canada, the Czech Republic, China, Ethiopia, Turkey, the Netherlands, Japan, Spain, the Philippines, Germany, Portugal, Israel, Korea, Russia, and Australia (Digman & Shmelyov, 1996; Katigbak et al., 2002; McCrae et al., 2005; Somer & Goldberg, 1999). One monumental research venture gathered data from thousands of people across 50 cultures. In this massive project as in many smaller ones, the five personality factors emerged whether people were asked for self-reports or were assessed by others (McCrae et al., 2005; Terracciano & McCrae, 2006).

Although the Big Five are quite stable over a lifetime, they are influenced by universal processes of maturation and aging. Data from an enormous cross-sectional sample involving more than 1.2 million children, adolescents, and adults, ages 10 to 65, revealed that whereas adult trends are overwhelmingly in the direction of greater maturity and adjustment, maturity plummets between late childhood and adolescence (Soto et al., 2011). Another survey of thousands of people in 10 countries, and a meta-analysis of 92 longitudinal studies, found that young people, ages 16 to 21, are the most neurotic (emotionally negative) and the least agreeable and conscientious. But there is good news for crabby, irresponsible neurotics, especially young ones. As you can see in Figure14.1, people tend to become more agreeable, conscientious, and emotionally stable between ages 30 and 40 (Bleidorn et al., 2013; Costa et al., 1999; Roberts, Walton, & Viechtbauer, 2006). The slow, steady rise of conscientiousness over the lifespan, a change that is found in many countries, suggests that this trait is associated with maturation. In their later years, people also tend to become less extroverted and less open to new experiences (Roberts & Mroczek, 2008; Specht, Egloff, & Schmukle, 2011).

Experience, too, shapes personality traits. For example, extroverts obviously seek out certain experiences that shy people might not, but after people are in a situation that brings out qualities they did not know they had, their traits may be modified accordingly (Specht et al., 2011). Those situations can change with social and economic conditions. A large group of women, graduates of Mills College, was followed from college until their 70s—quite an undertaking by investigators! When these women were young, in the 1960s, they led constrained lives that were highly gender stereotyped. As a result, at that time their personality traits did not predict their work or educational experiences—extroverts and introverts alike were behaving conventionally in their choices of family and work. But as gender roles changed and opportunities for women opened up in society at large, individual personality traits took on more power to predict the behavior of these women. In particular, the traits of extroversion, conscientiousness, and openness to experience came to be better predictors of the kind of work the women were doing and how satisfied they were feeling in their middle and later years (George, Helson, & John, 2011).

The Big Five do not provide a complete picture of personality, of course. Clinical psychologists note that various traits involved in mental disorders are missing, such as psychopathy (lack of remorse and empathy), self-absorption, impulsivity, and obsessiveness (Westen & Shedler, 1999). Personality researchers note that other significant traits are missing, such as religiosity, dishonesty, humorousness, independence, and conventionality (Abrahamson, Baker, & Caspi, 2002; Paunonen & Ashton, 2001). But most agree that the Big Five do lie at the core of key personality variations among individuals, and not only human individuals, either, as we are about to see.