The 'IQ' factor: implications for intelligence theory and measurement

The history of intelligence test development is considered with special ref erence to the drift away; from verbal tests and to the contemporary assumpt ion that every factor produced by statistical analysis of cognitive perform ance variables is an 'intelligence' factor. To test this assumption of univ ersal test validity the Wechsler Adult Intelligence Scale (WAIS) and Raven' s Advanced Progressive Matrices (RAPM) test were administered to 76 subject s, with equal numbers of males and females and ages representing the whole adult life-span. Principal components analyses (PCA) and multiple linear re gression analyses (MLR) demonstrated that age and sex account for 3% of the variance of IQ scores' as compared to 1, 28 and 64% for Cattell's 'Gc','Gs ar', and 'Gf factors, respectively. In addition, with IQ as a marker variab le, and including age and sex, PCA was used to ascertain factor loadings fo r IQ on the three G factors, The highest loading of 0.77 was found for Gc w hereas the loadings for Gsar and Gf were only 0.31 and 0.19, respectively. These results support the conclusion that while there are multiple cognitiv e performance factors there is only one IQ factor and therefore only one va lid intelligence factor. Theoretical, social and research implications are discussed. (C) 1999 Elsevier Science Ltd. All rights reserved.