Speeded testing in the assessment of intelligence gives rise to a speed factor

This paper reports an investigation of whether data on intelligence obtained by speeded testing have to be represented in confirmatory factor analysis (CFA) by an additional factor besides the ability factor, and whether the additional factor can be identified as a speed factor. The paper further examined whether the hypothesized speed factor influences the relationship between intelligence and working memory. Two independent datasets including data obtained by speeded intelligence testing, measures of processing speed and of working memory were investigated by means of CFA. A hybrid bifactor model was employed to represent the hypothesized speed and the ability factor of the intelligence data. Whereas the factor loadings for representing ability were set free for estimation, the factor loadings for representing speed were constrained according to theory-based expectations. The results showed that a speed factor is necessary for achieving a good fit to the data with speeded testing. The convergent validity of the speed factor was shown by data on measures of processing speed. Furthermore, it turned out that the consideration of the latent speed factor led to a decrease of the correlation between intelligence and working memory. These results suggest that speeded testing influences the assessment of intelligence and may also bias empirical findings regarding the relationships between intelligence and other constructs.