Three stratum theory

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Presented by John Carroll 1993 in "Human cognitive abilities: A survey of factor-analytic studies",[1][2] the hierarchical Three-Stratum Theory of cognitive abilities is based on a factor analytic study of correlation of individual differences variables from measures including psychological tests, school marks, and competence ratings. These factor analyses suggested three layers or strata, with each layer accounting for the variation in correlations among elements at the next lower level.

The three strata are defined as representing narrow, broad, and general cognitive ability. The factors describe stable and observable differences among individuals in the performance of tasks. Carroll argues further that they are not mere artifacts of a mathematical process, but likely reflect physiological factors explaining differences in ability (e.g., nerve firing rates). This of course does not alter the effectiveness of factor scores in accounting for behavioral differences.

Carroll proposes a taxonomic dimension in the distinction between level factors and speed factors. The tasks that contribute to the identification of level factors can be sorted by difficulty and individuals differentiated by whether they have acquired the skill to perform the tasks. Tasks that contribute to speed factors are distinguished by the relative speed with which individuals can complete them. Carroll suggests that the distinction between level and speed factors may be the broadest taxonomy of cognitive tasks that can be offered. Carroll distinguishes his hierarchical approach from taxonomic approaches such as Guilford’s Structure of Intellect model (three-dimensional model with contents, operations, and products).

Carroll's three-stratum model. Key: fluid intelligence (Gf), crystallized intelligence (Gc), general memory and learning (Gy), broad visual perception (Gv), broad auditory perception (Gu), broad retrieval ability (Gr), broad cognitive speediness (Gs), and processing speed (Gt). Carroll regarded the broad abilities as different "flavors" of g.


  1. ^ J. B. Carroll. (1993). Human cognitive abilities: A survey of factor-analytic studies. Cambridge University Press, New York, NY, USA.
  2. ^ J. B. Carroll (1997). The three-stratum theory of cognitive abilities. In Contemporary intellectual assessment: Theories, tests, and issues. D. P. Flanagan, J. L. Genshaft and et al., New York, NY, USA, Guilford Press, 122-130]

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