Correlates of some curious regressions on a measure of intelligence

Abstract

In the course of a methodological investigation of regressions of means of selected tests, computed in stratified levels of a general intelligence composite, on the mean levels of intelligence within the strata we encountered curious phenomena at the low end of the distribution of intelligence. At about -2.00 SD units of that distribution, the regressions of the vocabulary means for both boys and girls turned abruptly upwards, while those for mechanical reasoning dropped sharply. To investigate these curious regressions, we formed high and low vocabulary groups for each sex within the low-scoring subsample of general intelligence, and the means of the four groups on a series of cognitive and self-report scales were obtained. In this sample the high school boys and girls who are high in vocabulary relative to their low scores on the intelligence composite have lower means than their low-low controls on a set of cognitive tests epitomized by visualization in three dimensions, but the set also includes verbal tests in which the tasks are ambiguous and require inference and hypothesis formation in order to obtain a solution. Correct answers are not directly present in long-term memory as they are for the academic (including mathematics) and nonacademic information tests, on which the two high vocabulary groups are substantially superior. The high and the low vocabulary groups also differ from each other in health histories, personality traits, vocational interests, and biographical data scores, the high groups being consistently closer to the norm for their high school class. Sex differences are minimal in the incidence of the deficit and in its correlates. A genetic explanation for the problem is plausible, but the locus is not on the 23rd pair of chromosomes.