A note on general intelligence and the MA deviation concept

Restraints are imposed on the fullest emergence of g when subjects of equal chronological age are drawn from a restricted range of intelligence, or when groups representing different levels of IQ are factor-analyzed separately. Realistically, persons representing the extremes of intelligence cannot be included in the same study unless they are approximately equated on mental age (MA), in which case the relative performances of the extreme groups can provide useful information about the nature of intelligence. Comparisons of less extreme groups (e.g., average vs intellectually retarded or gifted) are also informative, particularly when attention is given to the types of tasks on which the retarded show the largest MA lag and the gifted show the largest MA acceleration.