The Big Five personality model, unlike many personality systems, did not grow out of an individual psychologist's theory. Rather, several researchers approaching the problem of classifying personality discovered that the differences between people seemed to naturally sort themselves into five broad dimensions. As the evidence grew, the scientific community began to reach a consensus, agreeing that human personality is most accurately described in terms of these Big Five factors.
The Discovery of the Five Factors of Personality
One of the first scientific endeavors to hint at the existence of the Big Five involved studying the adjectives that we use to describe people. In the late 1800's, psychologist Sir Francis Galton used a dictionary to take an inventory of all the words that could be used to describe a person's character, with the goal of developing a taxonomy of personality traits.
His work was picked up in the 1930's by psychometrician LL Thurstone, who provided a set of subjects a list of 60 adjectives and asked them to rate a person close to them based on how well each adjective described them. Thurstone then applied the statistical method of factor analysis to analyze how the adjectives were related, and discovered that they clustered into five groups, which corresponded with the Big Five factors of personality. Later work by psychologists Gordon Allport and Henry Odbert expanded the classification of adjectives in an attempt to include every possible word that could be used to describe a person.
In the 1940's, researchers used Allport and Odbert's list of adjectives to attempt to build a taxonomy of personality. Again using factor analysis, psychologists including Raymond Cattell, Donald Fiske and Warren Norman investigated the relationships between the words we use to describe people. Although each researcher came to his own specific conclusions, the overall findings from this era pointed, again, to five broad categories of human personality.
Later in the twentieth century, new interest in psychometric instruments took Big Five research into a different direction. Researchers hoping to develop assessments that would be useful in job placement used the Big Five to construct personality scales. Using a variety of psychometric instruments to explore key aspects of personality, researchers confirmed that personality-related questionnaire items generally clustered into five groups. For instance, items such as "I tend to start conversations" and "I love large parties" tended to correlate with one another (as they are both related to Extraversion), but not with items such as "I stay organized" (related to Conscientiousness) or "I frequently feel anxious" (Neuroticism).
More recently, the Big Five model has been used to develop robust personality assessments for use in research, business, and personal development. As our understanding of the biological basis of psychology advances, we are also discovering how the Big Five personality factors correlate with brain function, neurotransmitter activity, and other physiological factors.