Eysenck's Criminal Personality Theory
Eysenck’s Criminal Personality Theory
Hans Eysenck argued that personality is biological, not just learned. His criminal personality theory (1964, 1992) claims that people are born with a nervous system that makes some more likely to break rules than others. Eysenck measured personality along three dimensions, often called the PEN model — psychoticism, extraversion and neuroticism.
Eysenck’s PEN model links three personality dimensions to criminality: high Psychoticism, high Extraversion and high Neuroticism. Each dimension has a biological basis in how the nervous system regulates arousal.
The Three Personality Dimensions
Extraversion describes people who are sociable, impulsive and crave stimulation. Eysenck argued that extraverts have naturally low levels of cortical arousal, so they seek excitement — including risk-taking and rule-breaking — to reach a normal arousal level.
Neuroticism describes people who are anxious, moody and react strongly to stress. Eysenck linked high neuroticism to a nervous system that reacts too quickly to stressors, meaning small pressures can trigger a big emotional response, making self-control harder in difficult situations.
Psychoticism describes people who are aggressive, cold and lacking in empathy. Eysenck linked high psychoticism mainly to high levels of testosterone (and low serotonin), which he connected to aggressive, low-empathy and antisocial behaviour. Of the three dimensions, high psychoticism has the strongest theoretical link to serious criminal behaviour.
The Biological Basis of Personality
Eysenck explained extraversion using arousal theory. The reticular activation system (RAS) regulates how alert we feel by sending signals to the cerebral cortex, the outer layer of the brain responsible for higher thinking. Eysenck proposed that extraverts have an RAS that produces lower baseline arousal in the cortex, so they are chronically under-stimulated and seek excitement through risk-taking, sensation-seeking and, in some cases, criminal behaviour.
Eysenck linked psychoticism chiefly to hormonal factors, especially high testosterone (with low serotonin also implicated). He argued higher testosterone was associated with the aggressive, cold, low-empathy and impulsive profile seen in high psychoticism scorers.
Neuroticism was explained through the autonomic nervous system (ANS) and the limbic system. Eysenck suggested that highly neurotic people have an ANS that reacts too quickly and too strongly to stressors, and a limbic system that amplifies emotional responses such as fear and anxiety. This makes self-control under pressure more difficult, which Eysenck linked to impulsive offending in stressful situations.
Eysenck’s biological explanations: the reticular activation system and cerebral cortex explain low arousal in extraversion; high testosterone (and low serotonin) explains psychoticism; the autonomic nervous system and limbic system explain neuroticism’s stress reactivity.
Eysenck also argued that socialisation depends on conditioning — children learn to avoid antisocial behaviour because it has been paired with unpleasant consequences, such as parental disapproval. Because extraverts are chronically under-aroused, Eysenck claimed they condition less easily: the anxiety response that normally makes a punishment “stick” is weaker in an extravert’s nervous system. This means extraverted children may take longer to learn moral restraint through normal upbringing, leaving them more likely to break rules as they grow older.
Research Study: Heaven (1996)
Background: Heaven investigated whether Eysenck’s personality dimensions, alongside self-esteem, could predict delinquent behaviour in teenagers over time.
Method: The study used a longitudinal design, testing the same group of adolescents on more than one occasion. Personality (including extraversion and psychoticism) and self-esteem were measured using self-report questionnaires, and delinquency was measured through self-report of antisocial acts.
Results and conclusions: Psychoticism showed a moderate association with delinquency measured at the same time (about 15% of the variance at Time 1), but it was a weak predictor of delinquency two years later (only about 4% of the variance at Time 2). Heaven concluded that personality dimensions were relatively weak longitudinal predictors of delinquency, offering only limited support for Eysenck's theory. The pattern for extraversion was weaker and less consistent, and self-esteem also played a role in predicting delinquent behaviour.
Criticisms: Self-report questionnaires rely on participants being honest about breaking rules, which may reduce validity through social desirability bias. As a correlational study, it cannot show that psychoticism causes delinquency — a third factor could explain both.
Criticisms of Eysenck’s Theory
A major criticism is the issue of individual differences: not every offender scores highly on psychoticism, extraversion or neuroticism, and many people with these traits never commit crime. This makes the theory difficult to apply to all criminals equally. The theory is also criticised for being biologically reductionist — it explains complex criminal behaviour mainly through nervous system differences, giving little weight to social or environmental factors such as upbringing, poverty or peer influence, which links to the wider nature/nurture debate in psychology.
Eysenck’s theory is criticised for individual differences — many offenders do not fit the personality profile — and for being reductionist, since it prioritises biology over social and environmental causes of crime.