Personality is a structure gathering interrelated behavioral, cognitive and emotional patterns that biological and environmental factors influence; these interrelated patterns are relatively stable over time periods, but they change over the entire lifetime. While there is no generally agreed-upon definition of personality, most theories focus on motivation and psychological interactions with the environment one is surrounded by. Trait-based personality theories, such as those defined by Raymond Cattell, define personality as traits that predict an individual's behavior. On the other hand, more behaviorally-based approaches define personality through learning and habits. Nevertheless, most theories view personality as relatively stable.
The study of the psychology of personality, called personality psychology, attempts to explain the tendencies that underlie differences in behavior. Psychologists have taken many different approaches to the study of personality, including biological, cognitive, learning, and trait-based theories, as well as psychodynamic, and humanistic approaches. The various approaches used to study personality today reflect the influence of the first theorists in the field, a group that includes Sigmund Freud, Alfred Adler, Gordon Allport, Hans Eysenck, Abraham Maslow, and Carl Rogers.
Personality can be determined through a variety of tests. Due to the fact that personality is a complex idea, the dimensions of personality and scales of such tests vary and often are poorly defined. Two main tools to measure personality are objective tests and projective measures. Examples of such tests are the: Big Five Inventory (BFI), Minnesota Multiphasic Personality Inventory (MMPI-2), Rorschach Inkblot test, Neurotic Personality Questionnaire KON-2006, or Eysenck's Personality Questionnaire (EPQ-R). All of these tests are beneficial because they have both reliability and validity, two factors that make a test accurate.