Hans Jürgen Eysenck (March 4, 1916 in Berlin, Germany - September 4, 1997 in London, UK) was a psychologist best remembered for his work on intelligence and personality, though he worked in a wide range of areas. At the time of his death, Eysenck was the living psychologist most frequently cited in science journals. 
Hans Eysenck was born in Germany, but moved to England as a young man in the 1930s because of his opposition to the Nazi party. Eysenck was the founding editor of the journal Personality and Individual Differences, and authored over 50 books and over 900 academic articles. He aroused intense debate with his controversial dealing with variation in IQ among racial groups (see race and intelligence).
Life and work
Eysenck was Professor of Psychology at the Institute of Psychiatry (IoP) from 1955 to 1983. He was a major contributor to the modern scientific theory of personality and a brilliant teacher who also played a crucial role in the establishment of behavioural treatments for mental disorders.
However, Eysenck's work was often controversial. Publications in which Eysenck's views have roused controversy include (chronologically):
- A paper in the 1950s  concluding that available data "fail to support the hypothesis that psychotherapy facilitates recovery from neurotic disorder".
- A chapter in Uses and Abuses of Psychology (1953) entitled "What is wrong with psychoanalysis".
- Race, Intelligence and Education (1971) (in the US: The IQ Argument)
- Sex, Violence and the Media (1978).
- Astrology - Science or Superstition? (1982)
- Smoking, Personality and Stress (1991)
By far the most acrimonious of the debates has been that over the role of genetics in IQ differences (See Genetics vs. environment), which led to Eysenck famously being punched on the nose during a talk at the London School of Economics.
Eysenck's attitude is summarised in his autobiography Rebel with a Cause (Transaction Publishers (1997), ISBN 1-56000-938-1): "I always felt that a scientist owes the world only one thing, and that is the truth as he sees it. If the truth contradicts deeply held beliefs, that is too bad. Tact and diplomacy are fine in international relations, in politics, perhaps even in business; in science only one thing matters, and that is the facts."
Eysenck's model of personality (P-E-N)
Eysenck was one of the first psychologists to study personality with the method of factor analysis, a statistical technique introduced by Charles Spearman. Eysenck's results suggested two main personality factors. The first factor was the tendency to experience negative emotions, and Eysenck referred to it as Neuroticism. The second factor was the tendency to enjoy positive events, especially social events, and Eysenck named it Extraversion. The two personality dimensions were described in his 1947 book Dimensions of Personality. It is common practice in personality psychology to refer to the dimensions by the first letters, E and N.
E and N provided a 2-dimensional space to describe individual differences in behaviour. An analogy can be made to how latitude and longitude describe a point on the face of the earth. Also, Eysenck noted how these two dimensions were similar to the four personality types first proposed by the Greek physician Hippocrates.
- High N and High E = Choleric type
- High N and Low E = Melancholic type
- Low N and High E = Sanguine type
- Low N and Low E = Phlegmatic type
The third dimension, psychoticism, was added to the model in the late 1970s, based upon collaborations between Eysenck and his wife, Sybil B. G. Eysenck, who is the current editor of Personality and Individual Differences.
The major strength of Eysenck's model was to provide detailed theory of the causes of personality. For example, Eysenck proposed that extraversion was caused by variability in cortical arousal: "introverts are characterized by higher levels of activity than extraverts and so are chronically more cortically aroused than extraverts". While it seems counterintuitive to suppose that introverts are more aroused than extraverts, the putative effect this has on behaviour is such that the introvert seeks lower levels of stimulation. Conversely, the extravert seeks to heighten his or her arousal to a more optimal level (as predicted by the Yerkes-Dodson Law) by increased activity, social engagement and other stimulation-seeking behaviours.
Comparison with other theories
The major alternative to Eysenck's three factor model of personality is a model that makes use of five broad traits, often called the Big Five model (see big five personality traits). The traits in the Big Five are as follows:
- Openness to experience
Extraversion and Neuroticism in the Big Five are similar to Eysenck's traits of the same name. However, what Eysenck calls the trait of Psychoticism corresponds to two traits in the Big Five model: Conscientiousness and Agreeableness. Eysenck's personality system did not address Openness to experience. He argued that his approach was a better description of personality (Eysenck, 1992a; 1992b).
Another important model of personality is that of Jeffrey Alan Gray, a former student of his.
Eysenck always insisted that his use of the term "extraversion" does not correspond to the usage adopted by Carl Jung, and has also challenged the popular belief that Jung coined the term.
Psychometric scales relevant to Eysenck's theory
Eysenck's theory of personality is closely linked with the scales that he and his co-workers developed. These include the Maudsley Medical Questionnaire, Eysenck Personality Inventory (EPI), Eysenck Personality Questionnaire (EPQ) and Sensation Seeking Scale (developed in conjunction with Marvin Zuckerman). The Eysenck Personality Profiler (EPP) breaks down different facets of each trait considered in the model. There has been some debate about whether these facets should include impulsivity as a facet of extraversion as Eysenck declared in his early work; or psychoticism. Eysenck declared for the latter, in later work.
Eysenck's later work
In 1994 he was one of 52 signatories on "Mainstream Science on Intelligence," an editorial written by Linda Gottfredson and published in the Wall Street Journal, which defended the findings on race and intelligence in The Bell Curve. 
Eysenck made early contributions to fields such as personality by express and explicit commitment to a very rigorous adherence to scientific methodology, as Eysenck believed that scientific methodology was required for progress in personality psychology. He used, for example, factor analysis, a rigorous statistical method, to support his personality model. His early work showed Eysenck to be an especially strong critic of psychoanalysis as a form of therapy, preferring behaviour therapy. Despite this strongly scientific interest, Eysenck was not shy, in later work, of giving attention to parapsychology and astrology. Indeed, he believed that empirical evidence supported the existence of paranormal abilities.
- Dimensions of Personality (1947)
- The Scientific Study of Personality (1952)
- The Structure of Human Personality (1952) and later editions
- Uses and Abuses of Psychology (1953)
- The Psychology of Politics (1954)
- Psychology and the Foundations of Psychiatry (1955)
- Sense and Nonsense in Psychology (1956)
- The Dynamics of Anxiety and Hysteria (1957)
- Perceptual Processes and Mental Illnesses (1957) with G. Granger and J. C. Brengelmann
- Manual of the Maudsley Personality Inventory (1959)
- Handbook of Abnormal Psychology (1960) editor, later editions
- Experiments in Personality (1960) two volumes, editor
- Behaviour Therapy and Neuroses (1960) editor
- Know Your Own I.Q. (1962)
- Experiments with Drugs (1963) editor
- Experiments in Motivation (1964) editor
- Crime and Personality (1964) and later editions
- Manual of the Eysenck Personality Inventory (1964) with S. B. G. Eysenck
- The Causes and Cures of Neuroses (1965) with S. Rachman
- Fact and Fiction in Psychology (1965)
- Smoking, Health and Personality (1965)
- Check Your Own I.Q. (1966)
- The Effects of Psychotherapy (1966)
- The Biological Basis of Personality (1967)
- Eysenck, H.J. & Eysenck, S.B.G. (1969). Personality Structure and Measurement. London: Routledge.
- Readings in Extraversion/Introversion (1971) three volumes
- Race, Intelligence and Education (1971) in US as The IQ Argument
- Psychology is about People (1972)
- Lexicon de Psychologie (1972) three volumes, with W. Arnold and R. Meili
- The Inequality of Man (1973)
- Eysenck on Extraversion (1973) editor
- The Measurement of Intelligence (1973) editor
- The Experimental Study of Freudian theories (1973) with G. D. Wilson
- Case Histories in Behaviour Therapy (1974) editor
- Know Your Own Personality (1975) with G. D. Wilson
- Manual of the Eysenck Personality Questionnaire (1975) with S. B. G. Eysenck
- A Textbook of Human Psychology (1976) with G. D. Wilson
- Sex and Personality (1976)
- The Measurement of Personality (1976) editor
- Eysenck, H.J. & Eysenck, S.B.G. (1976). Psychoticism as a Dimension of Personality. London: Hodder and Stoughton.
- Reminiscence, Motivation and Personality (1977) with C. D. Frith
- You and Neurosis (1977)
- Die Zukunft der Psychologie (1977)
- The Psychological Basis of Ideology (1978) editor, with G. D. Wilson
- Sex Violence and the Media (1978) with D. Nias
- The Structure and Measurement of Intelligence (1979)
- The Psychology of Sex (1979) with G. D. Wilson
- The Causes and Effects of Smoking (1980)
- A Model for Personality (1981) editor
- Mindwatching (1981) with M. W. Eysenck, and later editions
- The Battle for the Mind (1981) with L. J. Kamin, in US as The Intelligence Controversy
- Personality, Genetics and Behaviour (1982)
- Explaining the Unexplained (1982) with Carl Sargent
- H.J. Eysenck & D.K.B. Nias, Astrology: Science or Superstition? Penguin Books (1982) ISBN 0-14-022397-5
- A Model for Intelligence (1982) editor
- Know Your Own Psi-Q (1983) with Carl Sargent
- …'I Do'. Your Happy Guide to Marriage (1983) with B. N. Kelly
- Personality and Individual Differences: A Natural Science Approach (1985) with M. W. Eysenck
- Decline and Fall of the Freudian Empire (1985)
- Rauchen und Gesundheit (1987)
- Personality Dimensions and Arousal (1987) editor, with J. Strelau
- Theoretical Foundations of Behaviour Therapy (1988) editor, with I. Martin
- The Causes and Cures of Criminality (1989) with G. H. Gudjonsson
- Genes, Culture and Personality: An Empirical Approach (1989) with L. Eaves and N. Martin
- Suggestion and Suggestibility (1989) editor, with V. A. Gheorghiu, P. Netter, and R. Rosenthal
- Eysenck, H.J. (1992). A reply to Costa and McCrae. P or A and C - the role of theory. Personality and Individual Differences, 13, 867-868.
- Eysenck, H.J. (1992). Four ways five factors are not basic. Personality and Individual Differences, 13, 667-673.