Construct Validity of Raven's Advanced Progressive Matrices for African and Non‐African Engineering Students in South Africa

We test the hypothesis that the Raven's Advanced Progressive Matrices has the same construct validity in African university students as it does in non‐African students by examining data from 306 highly select 17‐ to 23‐year olds in the Faculties of Engineering and the Built Environment at the University of the Witwatersrand (177 Africans, 57 East Indians, 72 Whites; 54 women, 252 men). Analyses were made of the Matrices scores, an English Comprehension test, the Similarities subscale from the South African Wechsler Adult Intelligence Scale, end‐of‐year university grades, and high‐school grade point average. Out of the 36 Matrices problems, the African students solved an average of 23; East Indian students, 26; and White students, 29 (p<.001), placing them at the 60th, 71st, and 86th percentiles, respectively, and yielding IQ equivalents of 103, 108, and 118 on the 1993 US norms. The same pattern of group differences was found on the Comprehension Test, the Similarities subscale, university course grades, and high‐school grade‐point average. The items on the Matrices ‘behaved’ in the same way for the African students as they did for the non‐African students, thereby indicating the test's internal validity. Item analyses, including a confirmatory factor analysis, showed that the African/non‐African difference was most pronounced on the general factor of intelligence. Concurrent validity was demonstrated by correlating the Matrices with the other measures, both individually and in composite. For the African group, the mean r=.28, p<.05, and for the non‐African group, the mean r=.27, p<.05. Although the intercepts of the regression lines for the two groups were significantly different, their slopes were not. The results imply that scores on the Raven's Matrices are as valid for Africans as they are for non‐Africans.     

Heritability of item responses on the Eysenck personality questionnaire

We report estimates of the heritabilities and common environment variances for the 90 items of the Eysenck Personality Questionnaire. Responses from 627 pairs of twins were analysed using the biometrical genetic analysis based on the threshold model described by Falconer. Many of the items revealed very substantial heritabilities. No less than 67/90 had heritabilities > 33%, 19 had > 50% and a few were even > 65%. Some of the useful implications of item heritabilities are discussed.     

Black–White differences on the g-factor in South Africa: a “Jensen Effect” on the Wechsler Intelligence Scale for Children — revised

A test is made to determine whether South African Black–White differences on various tests of cognitive performance are like the Black–White differences in the United States in being positively associated with a test's g loadings, where g is the general factor of intelligence. Data are analyzed from Skuy, Schutte, Fridjhon and O'Carroll [Skuy, M., Schutte, E., Fridjhon, P., & O'Carroll, S. (2001). Suitability of published neuropsychological test norms for urban African secondary school strudents in South Africa. Personality and Individual Differences, 30, 1413–1425) of 154 13- to 15-year-old secondary school students in Soweto, Johannesburg, on the Wechsler Intelligence Scale for Children–Revised (WISC-R). The more highly correlated a sub-test was with g, the more it predicted the African–White difference (r =0.77, p=0.05). The effect remained even when the Vocabulary sub-test was excluded or when g was extracted from the Black rather than from the White standardization sample (r=0.60, P<0.05), as it did as well if Spearman's rho was used instead of Pearson's r (g from Whites=0.74, g from Blacks=0.74, P< 0.005). Understanding observed Black–White differences around the world requires new research on the nature and nurture of g.     

Surface dependent segregation of Y2O3 in t-ZrO2

Atomistic simulation techniques have been used to predict the preferential segregation of Y³⁺ ions to the (100), (101) and (110) surfaces of tetragonal zirconia (t-ZrO₂). It is found that segregation energetics vary greatly between surfaces. In particular, dopant ions segregate to the top of the (101) surface. Conversely, although they also segregate towards the (100) and (110) surfaces, Y³⁺ becomes trapped just beneath these surfaces. For all of these surfaces, segregation effects are negligible below 12Å. The surface orientation dependence will result in significant variations in the concentration of yttrium at different surfaces. As a consequence, properties that are a function of defect concentration and distribution will be surface dependent. Predictive understanding of such segregation effects will provide the possibility of better engineered devices for a variety of thermal and electrochemical applications.     

Group-based interpersonal psychotherapy for posttraumatic stress disorder: theoretical and clinical aspects

Posttraumatic stress disorder (PTSD) is a condition that engenders both symptomatic distress and severe disruption in interpersonal and social functioning. Most of the empirical research on treatment has emphasized interventions that aim to alleviate the symptoms of PTSD, despite the persisting impairments in social, occupational, and interpersonal functioning. In clinical practice, achieving relief from symptoms such as irritability or phobic avoidance is a worthwhile goal, yet significant distress and disability derived from disruptions to interpersonal attachments, social networks, and confiding intimate relationships persist. Interpersonal psychotherapy (IPT) has been shown to be efficacious in research settings for depression and eating disorders, in both group and individual formats. Recent pilot data also suggests the potential usefulness of IPT in anxiety disorders. The aim of this paper is to provide a rationale for the use of group-based IPT as an intervention for PTSD as part of a management package, arguing from theoretical and clinical viewpoints. The integration of IPT therapeutic processes with the therapeutic group process is discussed, and a detailed case discussion is presented as an illustration.     

Mate choice and friendship in twins: evidence for genetic similarity

This study examined the genetic and environmental contribution to people's preference for spouses and friends to be similar to themselves. In their responses to 130 personality, attitude, and demographic questions, 174 pairs of monozygotic (MZ) twins resembled each other (r= .53) more than did 148 pairs of dizygotic (DZ) twins (r= .32), 322 pairs of spouses (r= .32), and 563 pairs of best friends (r= .20). It was not previously recognized that spouses and friends are as similar as DZ twins. MZ twins also chose spouses and best friends more similar to their co-twins' friends and spouses than did DZ twins (mean rs = .22 vs. .14). The twins' preference for spouses and friends similar to themselves was about 34% due to the twins' genes, 12% due to the twins' common environment, and 54% due to the twins' unique (nonshared) environment. Similarity to partners was more pronounced on the more heritable items than the less heritable items. It is concluded that people are genetically inclined to choose as social partners those who resemble themselves at a genetic level.     

Relation between aging and rated teaching effectiveness of academic psychologists

Within a combined cross-sectional and longitudinal design, several analyses showed that student-rated teaching effectiveness in university professors declined with age. For 106 full-time psychology teachers, aged 26 to 55, who were studied for time periods ranging from 2 to 15 years, an overall negative correlation of r = -.33 (p less than .05) was found between age and general teaching effectiveness. A similar decrement with age occurred for items measuring specific teaching behaviors. Age accounted for 8% of the variance in general teaching effectiveness.     

The evolutionary selection of human races: A response to Miller

Miller's (1993, Personality and Individual Differences, 15, 665–675) theory of the origin of “the African Personality” is not new. The focus on testosterone as a mediator of male-male agonistic interaction and strong sexuality has been a component of the r-K analysis of human race differences from the outset. Several aspects of Miller's paper are discussed.     

Race, brain size, and intelligence: a reply to Cernovsky

Cernovsky's 1990 critique of my work on the relation between brain size and IQ inadequately presents my position. I did not address the issue of sex differences in brain size nor did I conclude that "women are less intelligent than men" (p. 337). In the autopsy study cited by Cernovsky, it was concluded that, when body size is controlled, the male-female difference in brain size is removed but the black-white difference in brain size remains. Cernovsky also ignores much additional data, including that Mongoloid populations have larger and heavier brains than Caucasoids. Here, I review evidence on the relation between (a) brain size and race and (b) brain size and intelligence. Data are also tabulated for personality, speed of maturation, and sexuality, on all of which the Caucasoid average consistently falls between those of Mongoloids and Negroids. This ordering may be explained by a gene-based evolutionary theory of r/K reproductive strategies in which Mongoloids are more K-selected than Caucasoids and Caucasoids more than Negroids.