A and Type B personality theory: During the 1950s, Meyer Friedman and his co-workers defined what they called Type A and Type B behavior patterns. They theorized that intense, hard-driving Type A personalities had a higher risk of coronary disease because they are "stress junkies." Type B people, on the other hand, tended to be relaxed, less competitive, and lower in risk. There was also a Type AB mixed profile. John L. Holland's RIASEC vocational model, commonly referred to as the Holland Codes, stipulates that six personality types lead people to choose their career paths. In this circumplex model, the six types are represented as a hexagon, with adjacent types more closely related than those more distant. The model is widely used in vocational counseling. Eduard Spranger's personality-model, consisting of six (or, by some revisions, 6 +1) basic types of value attitudes, described in his book Types of Men (Lebensformen; Halle (Saale): Niemeyer, 1914; English translation by P. J. W. Pigors - New York: G. E. Stechert Company, 1928). The Enneagram of Personality, a model of human personality which is principally used as a typology of nine interconnected personality types. It has been criticized as being subject to interpretation, making it difficult to test or validate scientifically. Perhaps the most ancient attempt at personality psychology is the personality typology outlined by the Indian Buddhist Abhidharma schools. This typology mostly focuses on negative personal traits (greed, hatred, and delusion) and the corresponding positive meditation practices used to counter those traits. Psychoanalytical theories Psychoanalytic theories explain human behavior in terms of the interaction of various components of personality. Sigmund Freud was the founder of this school of thought. He drew on the physics of his day (thermodynamics) to coin the term psychodynamics. Based on the idea of converting heat into mechanical energy, Freud proposed psychic energy could be converted into behavior. His theory places central importance on dynamic, unconscious psychological conflicts. Freud divides human personality into three significant components: the id, ego and super-ego. The id acts according to the pleasure principle, demanding immediate gratification of its needs regardless of external environment; the ego then must emerge in order to realistically meet the wishes and demands of the id in accordance with the outside world, adhering to the reality principle. Finally, the superego (conscience) inculcates moral judgment and societal rules upon the ego, thus forcing the demands of the id to be