IN THIS and the following chapter we shall review briefly the nature and occurrence of such psychological characteristics as have been measured by tests. In Part III we shall go into greater detail about the relationship between psychological test material and occupational selection, so far as it has been studied. Our purpose in this chapter is to accumulate background on the nature of these variables, their occurrence in the population generally, their interrelationships, and their broad relationships to occupations.
We shall discuss intelligence, special abilities, personality, and interests, and shall not stop every time to qualify these terms, to indicate that in each instance what we are talking about is not an abstract quality or trait in a substantive sense, but whatever it is that a particular psychological test tests. We draw certain inferences from tests regarding the psychological facts, but our raw data are tests or observations.
Tests referred to in this and later chapters will not be described beyond a brief indication of their character and purpose. The glossary, pp. 323-326, contains descriptions and sources for all tests.
Since intelligence tests were first developed, our concepts of the nature of intelligence have undergone considerable transformation, and there is still no very exact consensus. For some time we worked on the hypothesis that intelligence was general, independent, and substantive in nature, that any one person had just so much which could be measured, more or less accurately, and that this amount was, except in extraordinary circumstances, unalterable. Almost all these ideas have changed. We now speak of various "fac