Eysenck added a third dimension to the personality trait i.e. extraversion, neuroticism and psychoticism.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.