The nature of psychometric g: Unitary process or a number of independent processes?

Abstract

This study investigates whether a unitary elemental process or a number of independent elemental processes, as measured by elementary cognitive tasks (ECTs), underlie psychometric g. A sample of 101 university students was administered two intelligence tests (Raven's Advanced Progressive Matrices and the Multidimensional Aptitude Battery) and a large battery of ECTs. The results of this study reject the theory that some single or unitary process underlies psychometric g. Rather, it appears that individual differences in psychometric g may reflect as many as four independent components of variance. These findings support the theory that various complex mental tests correlate highly with each other, giving rise to a psychometric g factor, because they require some of the same elemental processes. Further research will be needed to determine precisely the number and nature of these components. It is also important to note that the multiple correlation of g regressed on these four components derived from elementary cognitive variables is .542. The maximum correlation possible between the psychometric variables and the battery of ECTs in this study is nearly as high as correlations among various standardized IQ tests themselves (canonical r=.603). After correction for the considerable restriction of range on IQ in the sample, the r is increased to .722. Hence, this battery of ECTs accounts for approximately half of the phenotypic variance in g and probably as much as 70% of the genotypic variance. Moreover, the finding that individual differences in conceptually distinct processes (such as speed of visual search and speed of memory search) are highly correlated indicates the presence of individual differences in some neurological level of processing common to both tasks.