Hans Eysenck was born in Germany but moved to England after turning 18 and spent most of his working life there. His research interests were wide-ranging, but he is perhaps best known for his theories of personality and intelligence.

Eysenck (1952, 1967, 1982) proposed a theory of personality based on biological factors, arguing that individuals inherit a type of nervous system that affects their ability to learn and adapt to the environment.

During 1940s Eysenck was working at the Maudsley psychiatric hospital in London. His job was to make an initial assessment of each patient before their mental disorder was diagnosed by a psychiatrist.

Through this position, he compiled a battery of questions about behavior, which he later applied to 700 soldiers who were being treated for neurotic disorders at the hospital (Eysenck (1947).

He found that the soldiers' answers seemed to link naturally with one another, suggesting that there were a number of different personality traits which were being revealed by the soldier's answers. He called these first-order personality traits

He used a technique called factor analysis. This technique reduces behavior to a number of factors which can be grouped together under separate headings, called dimensions.

Eysenck (1947) found that their behavior could be represented by two dimensions: Introversion / Extroversion (E); Neuroticism / Stability (N). Eysenck called these second-order personality traits. Each aspect of personality (extraversion, neuroticism and psychoticism) can be traced back to a different biological cause. Personality is dependent on the balance between excitation and inhibition process of the autonomic nervous system (ANS).

Eysenck's theory of personality focused on temperaments, which he believed were largely controlled by genetic influences. He utilized a statistical technique known as factor analysis to identify what he believed were the two primary dimensions of personality: extraversion and neuroticism. He later added a third dimension known as psychoticism.

Hans Eysenck was a personality theorist who focused on temperament—innate, genetically based personality differences. He believed personality is largely governed by biology, and he viewed people as having two specific personality dimensions: extroversion vs. introversion and neuroticism vs. stability. After collaborating with his wife and fellow personality theorist Sybil Eysenck, he added a third dimension to this model: psychoticism vs. socialization.

·       According to their theory, people high on the trait of extroversion are sociable and outgoing and readily connect with others, whereas people high on the trait of introversion have a higher need to be alone, engage in solitary behaviors, and limit their interactions with others.

·       In the neuroticism/stability dimension, people high on neuroticism tend to be anxious; they tend to have an overactive sympathetic nervous system and even with low stress, their bodies and emotional state tend to go into a flight-or-fight reaction. In contrast, people high on stability tend to need more stimulation to activate their flight-or-fight reaction and are therefore considered more emotionally stable.

·       In the psychoticism/socialization dimension, people who are high on psychoticism tend to be independent thinkers, cold, nonconformist, impulsive, antisocial, and hostile. People who are high on socialization (often referred to as superego control) tend to have high impulse control—they are more altruistic, empathetic, cooperative, and conventional.

The major strength of Eysenck’s model is that he was one of the first to make his approach more quantifiable; it was therefore perceived to be more “legitimate”, as a common criticism of psychological theories is that they are not empirically verifiable. Eysenck proposed that extroversion was caused by variability in cortical arousal, with introverts characteristically having a higher level of activity in this area than extroverts. He also hypothesized that neuroticism was determined by individual differences in the limbic system, the part of the human brain involved in emotion, motivation, and emotional association with memory. Unlike Allport’s and Cattell’s models, however, Eysenck’s has been criticized for being too narrow.

Eysenck’s 3 Dimensions of Personality

British psychologist Hans Eysenck developed a model of personality based upon just three universal trails.

Extraverts are sociable and crave excitement and change, and thus can become bored easily. They tend to be carefree, optimistic and impulsive. They are more likely to take risks and be thrill seekers. Eysenck argues that this is because they inherit an under aroused nervous system and so seek stimulation to restore the level of optimum stimulation.

Introverts on the other hand lie at the other end of this scale, being quiet and reserved. They are already over-aroused and shun sensation and stimulation. Introverts are reserved, plan their actions and control their emotions. They tend to be serious, reliable and pessimistic.


A person’s level of neuroticism is determined by the reactivity of their sympathetic nervous system. A stable person’s nervous system will generally be less reactive to stressful situations, remaining calm and level headed.

Someone high in neuroticism on the other hand will be much more unstable, and prone to overreacting to stimuli and may be quick to worry, anger or fear. They are overly emotional and find it difficult to calm down once upset. Neurotic individuals have an ANS that responds quickly to stress.

Eysenck (1966) later added a third trait / dimension - Psychoticism – e.g., lacking in empathy, cruel, a loner, aggressive and troublesome. This has been related to high levels of testosterone. The higher the testosterone, the higher the level of psychoticism, with low levels related to more normal balanced behavior.

He was especially interested in the characteristics of people whom he considered to have achieved their potential as individuals.

According to Eysenck, the two dimensions of neuroticism (stable vs. unstable) and introversion-extroversion combine to form a variety of personality characteristics.

Eysenck traits theory of personality

Critical Evaluation

Twin studies can be used to see if personality is genetic. However, the findings are conflicting and non-conclusive.

Shields (1976) found that monozygotic (identical) twins were significantly more alike on the Introvert – Extrovert (E) and Psychoticism (P) dimensions than dizygotic (non-identical) twins.

Loehlin, Willerman, and Horn (1988) found that only 50% of the variations of scores on personality dimensions are due to inherited traits. This suggests that social factors are also important.

One good element of Eysenck’s theory is that it takes into account both nature and nurture. Eysenck’s theory argues strongly that biological predispositions towards certain personality traits combined with conditioning and socialization during childhood in order to create our personality.

This interactionist approach may, therefore, be much more valid than either a biological or environmental theory alone.

It also links nicely with the diathesis-stress model of behavior which argues for a biological predisposition combining with an environmental trigger for a particular behavior.