Trait Theory is what you are familiar with if you have taken nearly any Internet personality test. Trait theorists use a statistical technique known as factor analysis to determine relationships among the responses to diverse questionnaire items. In its current most popular formulation, trait theory embraces the "Big 5" traits (Extraversion, Agreeableness, Openness, Conscientiousness, and Neuroticism) as the most important determinants of behavior. There are various tests to determine peoples' quantitative rankings on these traits as well as their subtraits, called facets that agree to greater or lesser degrees. And of course, there are competing lists of traits, such as Hans Eysenck's three-factor theory (extraversion, neuroticism, and psychoticism) or Raymond B. Cattell's 16 P.F., a popular set of 16 traits.
- Structure: The unit of structure is the personality trait, or stable dispositional trend.
- Process: Traits can be seen as dynamic and interactive with one another, but trait theorists tend to concern themselves with measurements on questionnaires and statistical correlations.
- Growth and Development: Heredity and Environment, or Nature versus Nurture, is a big issue here. To what extent traits are inherited and to what extent they are determined by environmental factors has been studied in a variety of ways. The most successful have been twin studies, where either fraternal twins who are not genetically the same but who share many life experiences, or identical twins raised by different families are compared in order to test the heritability of particular traits. Of course, both have an effect. One finding of interest is that the unshared environment of siblings usually has a much greater effect on their development than their shared environment.
- Psychopathology: The model of psychopathology in trait theory is one of extreme scores in one or more trait dimensions. Hence an extremely conscientious person may be considered obsessive-compulsive, an extremely neurotic person may be considered, well, extremely neurotic, and so on.
- Change: Trait theory does not address change to a significant degree.