Jensen Effects among African, Indian, and White engineering students in South Africa on Raven's Standard Progressive Matrices

Abstract

Low test scores are routinely observed in sub-Saharan African populations. In this paper, we explore the topic further by examining Rushton and Skuy's [Intelligence 28 (2000) 251] hypothesis that a bimodal distribution exists in the African population with a high-scoring group virtually indistinguishable from Whites, and a low-scoring group performing significantly below both Whites and the higher-scoring African group. To test this hypothesis, we sought out a potentially higher-scoring African population than has previously been studied. We administered untimed Raven's Standard Progressive Matrices (SPM) to 342 17- to 23-year-olds in the Faculties of Engineering and the Built Environment at the University of the Witwatersrand in Johannesburg (198 Africans, 86 Whites, 58 Indians; 71 women, 271 men). Out of the 60 total problems, the African students solved an average of 50, the Indian students, 53, and the White students, 56 ( P<.001). On the 1993 US norms, Africans were at the 41st percentile, Indians at the 55th, and Whites at the 75th, with IQ equivalents of 97, 102, and 110, respectively. The African–Indian–White differences were most pronounced on those items with the highest item-total correlations, indicating a difference in g, or the general factor of intelligence. Hence, they were “Jensen Effects.” Indeed, the g loadings showed a small degree of cross-cultural generality; for example, item-total correlations calculated on the Indian students predicted the magnitude of the White–African differences. When the 60 items were aggregated into 10 “subtests,” the magnitude of the Jensen Effect was similar to that from previous studies based on whole subtests (median ρ=.53). There were no sex differences. Nor did this study of African engineering students support the idea of a bimodal distribution.