Differentiation at higher levels of cognitive ability: evidence from the United States.

Most psychologists and educators assume that intelligence is a linear construct, meaning that smart people simply have more intelligence than their less gifted peers. Likewise, individuals with mental retardation are thought to have less intelligence. In contrast to this widely accepted belief, the authors posed an alternative hypothesis--that intelligence is qualitatively different in various populations. Using factor analysis of a standardization sample of the Woodcock-Johnson Test of Cognitive Ability (R. W. Woodcock & M. B. Johnson, 1989), the authors examined the nature of intellect across ability. Results indicated that the amount of variance attributable to Spearman's g declined as measured intellectual ability increased.