ABSTRACT
THE notion of ‘validity’ is an interesting as well as an important one in psychology, and the misunderstandings attaching to it are legion. Textbooks often define it as the agreement between a test and some true measure of the property which the test is designed to measure, but of course it is only in trivial cases that such an outside criterion is in fact available. If we had a true measure of intelligence, or extraversion, or neuroticism, then we would hardly need to bother with less reliable and less valid tests of these properties; we would simply use the criterion itself. Thus we are obviously thrown back on other measures of validation and there is no agreement as to how precisely this should be done. This state of affairs is often contrasted unfavourably with that obtaining in physics where it is believed that the problem of validity hardly arises.
