Eysenck's Personality Questionnaire (EPQ): Eysenck's Three Dimensions of Personality Theory

Psychologist Hans Jürgen Eysenck created this EPQ (Eysenck Personality Questionnaire) model together with his wife Sybil B. G. Eysenck in 1947, which was updated again in the late 1970s. 

The personality model assumes that everyone is rooted on the similar three universal traits (PEN inventory):

1. Psychoticism versus Socialisation

When an individual is high on psychoticism scale, he/she exhibits hostile, antisocial, manipulative, and apathetic tendencies. They tend to find difficulties in dealing with reality. 

2. Extraversion versus Intraversion

Introversion as explained by Eysenck refers to a preferred way of individual to directs his/her attention to inner experiences, which commonly result to the individual being quieter and more reserved. 

Extraversion, on the other hand, is when individual directs the attention outward to people around them and to the environment. Someone who is higher on the extraversion scale will be more outgoing and sociable. High on positive affects, and requiring more external stimuli. 

3. Neuroticism versus Emotional stability

According to Eysenck, neuroticism relates to one's propensity to get emotional or become upset, while people who score high on the emotional stability bar stay emotionally constant. 

The general description for each PEN personality inventory:

Psychoticism	Extraversion	Neuroticism
Aggressive	Sociable	Anxious
Assertive	Irresponsible	Depressed
Egocentric	Dominant	Guilt Feelings
Unsympathetic	Lack of reflection	Low self-esteem
Manipulative	Sensation-seeking	Tense
Achievement-oriented	Impulsive	Moody
Dogmatic	Risk-taking	Hypochondriac
Masculine	Expressive	Lack of autonomy
Tough-minded	Active	Obsessive

From nature vs nurture point of view, Eysenck focuses more on the nature part, assuming that individuals temperament originates from the genetic inheritance. He considers personality differences as growing out of hereditary nature. 

Eysenck explains his personality model as highly determined by the activity in our nervous system (our physiology and genetics). 

Extraversion-intraversion is caused by differences in level of internal cortical arousal and level of external stimuli required to achieve individual's optimal performance. 

Emotional stability-instability is caused by differences in activation threshold. Neurotic possesses low activation threshold hence negative experience more easily incites anxiety, while the emotionally stable individual owns high activation threshold that enables him/her to stay calm and composed during problems. 

Psychoticism is caused by testosterone. High level of psychoticism is said to be caused by high level of testosterone.