ABSTRACT
The ego strength, source trait seems by contrast to be a partly acquired general dynamic trait producing an ability to mediate successfully between impulse and the opportunities of the external world. The advantages of using source traits in practical psychological measurements by means of the 'specification equation' are many – some obvious, some subtle. If the psychologist does not use source trait measures his main alternative is to make up what are called 'special purpose tests'. The scientific advantage of basing personality measurement on source traits rather than ad hoc 'scales' made up to each experimenter's predilections should need no further illustration. Source traits can be recognized across different age levels and cultures with minor modifications. Finally, they constitute concepts in psychology of basic theoretical importance, like affectothymia, intelligence, ego strength, surgency, and super-ego strength, around which the science of personality development is increasingly being built.
