The idea of dividing people by traits can be traced back as far as Hippocrates. In more modern times, we can look to Allport, Cattell, and others in order to understand trait theory in personality. Traits are variables or dimensions which are continuous. According to the Diagnostic and Statistical Manual (DSM) of the American Psychiatric Association, personality traits are prominent aspects of personality that are exhibited in a wide range of important social and personal contexts. In other words, individuals have certain characteristics which partly determine their behavior. An example of a trait is extraversion-introversion. Extraversion tends to be manifested in outgoing, talkative, energetic behavior, whereas introversion is manifested in more reserved and solitary behavior. An individual may fall along any point in the continuum, and the location where the individual falls will determine how an individual will responds in various contexts .
Gordon Allport was one of the first modern trait theorists. Allport and Henry Odbert worked through two of the most comprehensive dictionaries of the English language available and extracted around 18,000 personality-describing words. From this list they reduced the number of words to approximately 4500 personality-describing adjectives which they considered to describe observable and relatively permanent personality traits.
Allport organized traits into a hierarchy of three levels:
- Cardinal traits: These traits that dominate and shape an individual's behavior. They lie at the top of the hierarchy and are together known as the individual's master control.
- Central traits: These traits fall next in the hierarchy. These are general characteristics found in varying degrees in every person. They are the basic building blocks that shape most of our behavior. These traits are the types of things we might list in a letter of recommendation for a friend. An example of a central trait would be honesty.
- Secondary trait: Lying at the bottom of the hierarchy, these traits are plentiful, but activated by specific stimuli. These secondary traits explain why at times a person may exhibit behaviors which seem incongruent with other behaviors. Each seemingly inconsistent behavior is governed by a secondary trait, but both may be perfectly congruent with a central trait.
In 1946 Raymond Cattell took a list of 4500 traits, and removed all the synonyms, reducing the number down to 171. He then asked individuals to rate people whom they knew by the adjectives on the list. Using factor analysis, Cattell generated sixteen dimensions of human personality traits: abstractedness, warmth, apprehension, emotional stability, liveliness, openness to change, perfectionism, privateness, intelligence, rule consciousness, tension, sensitivity, social boldness, self-reliance, vigilance, and dominance. Cattell's 16 PF personality inventory is still in use today.
Hans Eysenck also has a personality inventory that is still used today. Eysenck's theory of personality is based along two dimensions: emotional stability and introversion/extroversion. These two dimensions are considered high level super-traits, and intersect to form four categories. The traits which fall within each of the four categories are low level traits.
The five-factor model was reached independently by several different psychologists over a number of years. Many psychologists believe that the number of traits can be reduced to five factors, and that all of the other traits fit within each of the five factors. Since the five-factor model was developed independently by a number of psychologists, the names of each of the five factors, and what each factor measures, differ according to theorist. The acronym OCEAN is often used to recall the five factors, and comes from Paul Costa's and Robert McCrae's conceptualization: Openness to Experience, Conscientiousness, Extraversion, Agreeableness, and Neuroticism.