General Intelligence and Special Aptitudes

Abstract

We have so far acquired some insight into the nature of cognitive tests which might, on theoretical grounds, be considered likely candidates for the measurement of intelligence; we must now turn to a consideration of that part of the theory which asserts that intelligence is the general or all-round cognitive ability which mediates success in such tests whatever their nature. Spearman has called this “the indifference of the indicator”; in other words, if a test or test item fulfils the conditions for a “good” test or test item laid down in his laws of neogenesis, then it should not matter much which item or test was chosen for the measurement. This implication of the theory can of course be investigated empirically, and methods for doing this were worked out by members of the London school - Karl Pearson, the great statistician, Charles Spearman himself, and Sir Cyril Burt, who succeeded Spearman in the professorial chair at University College, London. These methods are essentially based on the use of correlation coefficients, and on factor analysis, i. e. the analysis of sets of such coefficients. There are some statistical complexities to analyses of this kind, but these are inevitably outside the scope of this chapter; there are many good books dealing with the technique of factor analysis (Thomson, 1939; Burt, 1940, and Thurstone, 1947, are three classics; among modern texts are Harman, 1967, Pawlik, 1971 and Lawley and Maxwell, 1971).

No human investigation can be called real science if it cannot be demonstrated mathematically. Leonardo da Vinci