They show that roughly two-thirds of a group of neurotic patients will recover or improve to a marked extent within about two years of the onset of their illness, whether they are treated by means of psychotherapy or not.

G. Conversely the extravert seeks to heighten his or her arousal to a more favourable level (as predicted by the Yerkes-Dodson Law) by increased activity social engagement and other stimulation-seeking behaviors. He received his PhD in 1940 from University College London (UCL) working in the Department of Psychology under the supervision of Professor Sir Cyril Burt with whom he had a tumultuous professional relationship throughout his working life.

At the time of his death Eysenck was the living psychologist most frequently cited in science journals. Hans Jürgen Eysenck (4 March 1916 – 4 September 1997) was a psychologist born in Germany who spent his professional career in Great Britain.