Additional grounds for proposing that the “verbal” or “Gc” factor is the most valid intelligence factor

Robinson (1999) used WAIS IQ as an intelligence criterion to test the hypothesis that the “verbal” or “Gc” factor is more closely aligned with intelligence differences than the “non-verbal” “Gf” and “Gsar” factors. The results confirmed Robinson's hypothesis and also demonstrated that verbal measures are less likely to confound intelligence differences with age and sex differences. Subsequently, Ashton, Lee, and Vernon (2001) presented arguments opposed to Robinson's results and conclusions claiming, for example, that WAIS IQ is not an acceptable intelligence criterion and referring to alternative “popular”, “g factor” and “biological” criteria. The present article addresses the points raised by Ashton et al. It is concluded that the Ashton et al. arguments are conceptually flawed and factually incorrect, that analysis of the Ashton et al. MAB data and of WAIS standardization data provides additional support for the proposition that the “verbal” or “Gc” factor is the most valid intelligence factor, that the alternative intelligence criteria proposed by Ashton et al. are either very unreliable or totally invalid, and that there are no grounds for doubting the well-established status of the WAIS IQ intelligence criterion.