>The factors that provide the largest incremental validity over and above the criterion variance predicted by g are spatial and psychomotor abilities, which often contribute to the validity for predicting success in jobs requiring technical or motor skills. Physical scientists, for example, are well above average not only in g but also in spatial ability. Although most spatial tests are also quite g loaded, they can significantly enhance predictive validity for certain job categories.
Tests of psychomotor abilities also enhance validity for some jobs that depend on manual dexterity and muscular coordination. Considering how very different in form and content psychomotor tests are from the paper-and-pencil tests typically used to measure cognitive ability, it may seem surprising how relatively small the incremental validity contributed by psychomotor tests actually is, compared to the g validity even for jobs where psychomotor ability is relevant. The apparent reason for this is that the psychomotor tests are themselves largely tests of g, showing true-score correlations with g even as high as .70 after correction for range restriction in Air Force samples. Usually g accounts for most of the validity of psychomotor tests, thus allowing comparatively little incremental validity. (The expectation that a test’s appearance necessarily indicates what latent traits it measures has been called the “ topographical fallacy.” )
Major efforts to discover other psychometric variables that add appreciable increments over and above g to predictive validity for “core job performance” have not proved fruitful. Of course there are many other aspects of success in life besides g or spatial and psychomotor factors, such as physical and mental energy level, effort, conscientiousness, dependability, personal integrity, emotional stability, self-discipline, leadership, and creativity. These characteristics, however, fall into the personality domain and can be assessed to some extent by personality inventories. A person’s interests have little incremental validity over g or other cognitive abilities, largely because a person’s interests are to some degree related to the person’s abilities. People generally do not develop an interest in subjects or activities requiring a level of cognitive complexity that overtaxes their level of g. Specialized talents, when highly developed, may be crucial for success in certain fields, such as music, art, and creative writing. The individual’s level of g, however, is an important threshold variable for the socially and economically significant expression of such talents. Probably very few, if any, successful professionals in these fields have a below-average IQ.<
Arthur R. Jensen (1998)