Psychoticism is conceptually similar to the constraint factor in Tellegen's three-factor model of personality.
Costa and McCrae believe that agreeableness and conscientiousness (both of which represent low levels of psychoticism) need to be distinguished in personality models.
[3] It has also been suggested that "psychoticism" may be a misnomer and that "psychopathy" or "Impulsive Unsocialized Sensation Seeking" would be better labels.
[4] Other biological correlates of psychoticism include low conditionability and low levels of monoamine oxidase; beta-hydroxylase, cortisol, norepinephrine in cerebrospinal fluid also appear relevant to psychoticism level.
Eysenck's theoretical basis for the model was the theory of Einheitspsychosen (unitary psychosis) of the nineteenth-century German psychiatrist Heinrich Neumann.