Table 1.

Seven variables which determine the scores of individuals on intelligence tests (from Cattell et al., 1941, pp. 81–82).

For, if we agree to use the term intelligence and to speak of a single or compound “general ability,” the variations among individuals in their test scores in an intelligence test can be regarded as depending on:

(1)    Variations in the innate gene endowment which is responsible for the magnitude of this general ability, perhaps, e.g., in the genes defining the sum total of cerebral neurons. (G)

(2)    Variations in environmentally (i.e., post-conceptually) produced development of the general ability. (dG)

(3)    Variations in the closeness of the individual's cultural training and experience to the cultural medium in which the test is expressed. (c)

(4)    Variations in familiarity with tests and test situations, test training or “test sophistication.” Several slightly different and experimentally distinguishable types of preparedness are involved here. (t)

(5)    Fluctuations in the underlying general ability itself, through physiological, fatigue, and other variables. (f)

(6)    Fluctuations in the effective expression or application of the ability through varying strength and direction of volition and interest. (fv)

(7)    Chance errors in measurement not included in the above. (e)

Resorting to a formula, for facility in later discussions, we may say that any performance P in an intelligence test is a function of the factors in the following algebraic equation:

P = G + dG + c + t + f + fv + e + K, where K is a factor to cover special abilities.