Personality theorists usually get ever more adventurous as they set out empirically to test their ever more sophisticated theories. Most naturally begin in the laboratory, sometimes even the animal house, testing fundamental (biological and behavioural) tenets of the theory, which develops and changes as it is tested. However, demands both for ecological validity and applicability mean they soon find themselves testing theoretical assumptions on ‘real people in real settings’. These settings are most frequently the clinic, the classroom and the office/factory.

Any inspection of work of the trait theorists like Eysenck, Cattell and latterly Costa and McCrae shows how they usually first became interested in the clinical applications of their work, then the educational applications and finally the occupational and organizational applications. Perhaps because Eysenck was at the Institute of Psychiatry (though neither a trained nor practising clinician) he took a great deal of interest in clinical issues with all three dimensions (i.e., Extraversion, Neuroticism and Psychoticism) having obvious clinical implications. Being both a trained clinician and a student of Eysenck, it is no surprise that Jeffrey Gray too, chose to test many of his ideas first on rats and then on patients.

Raymond Cattell, of the three, seemed more interested in the educational sphere, both because of his educational training but also because of his work on intelligence. Similarly Hans Eysenck was always interested in learning theory and intelligence and always took an active interest in how both personality and intelligence predicted educational behaviours and outcomes.