The Standard Progressive Matrices (SPM) was administered to a sample of 592 16 year old school students in Libya. There was a small negative correlation of -0.14 between SPM scores and the number of siblings, indicating only marginal dysgenic fertility. Supplementary material giving the data is given online. (Contains 1 table.)

The Minnesota Study of Twins Reared Apart (MISTRA) was initiated in 1979 and continued until 2000. It consisted of 139 pairs of twins who had been separated in early childhood and not re-united until adulthood, and members of their families. As part of a broader assessment, these participants completed 42 mental ability tests from three well-known…

The aim of the study was to investigate the relationship between the Flynn effect and the effects of age differences between siblings on the intelligence difference between them. In Norway, the secular trends in intelligence-test score means vary both in magnitude and direction. We identified three periods: one period where the mean intelligence…

In old and even middle age, there are associations between physical health and both intelligence and education. This may occur because intelligence and/or education exert effects on lifestyle choices that, in turn, affect later health. Substance use is one aspect of lifestyle choice in young adulthood that could play such a role. The effects of…

The present study investigates the impact of changing fertility patterns on the Flynn effect. Intelligence test data comprised scores of army conscripts on an arithmetic, language and a Raven-similar test, and a composite score (General Ability). Family data of the conscripts enabled a decomposition of the population mean into effects of sibship…

We studied the age-related differences in inspection time and multiple cognitive domains in a group of monozygotic (MZ) and dizygotic (DZ) twins aged 7 to 17 years. Data from 111 twin pairs and 19 singleton siblings were included. We found clear age-related trends towards more efficient visual information processing in older participants. There…

To estimate Flynn effects (FEs) on forms of declarative memory (episodic, semantic) and visuospatial ability (Block Design) time-sequential analyses of data for Swedish adult samples (35-80 years) assessed on either of four occasions (1989, 1994, 1999, 2004; n = 2995) were conducted. The results demonstrated cognitive gains across occasions,…

There is scientific and popular dispute about whether there are sex differences in cognitive abilities and whether they are relevant to the proportions of men and women who attain high-level achievements, such as Nobel Prizes. A recent meta-analysis (Lynn, R., and Irwing, P. (2004). Sex differences on the progressive matrices: a meta-analysis.…

The relation between intelligence and birth order was shown in a recent publication [Bjerkedal, T., Kristensen, P., Skjeret, G. A. & Brevik, J. I. (2007). Intelligence test scores and birth order among young Norwegian men (conscripts) analyzed within and between families. "Intelligence," 35, 503-514] to be negative. Subjects in this…

The present paper reports the results of a within and between family analysis of the relation between birth order and intelligence. The material comprises more than a quarter of a million test scores for intellectual performance of Norwegian male conscripts recorded during 1984-2004. Conscripts, mostly 18-19 years of age, were born to women for…

SES has long interested researchers investigating school achievement. Its effects are often addressed by studying predictors of achievement in economically disadvantaged samples living primarily in biological families, confounding genetic and environmental influences. Little is known about SES's purely environmental effects. We measured them in…

This study examined the phenotypic and genotypic relationship between working memory speed (WMS) and working memory capacity (WMC) in 12-year-old twins and their siblings (N = 409). To asses WMS all children performed a reaction time task with three memory loads from which a basic mental speed measure and the derived slope were used. WMC was…

Genetic and environmental influences on academic achievement were studied for 314 pairs of white full siblings and 53 pairs of half siblings and 161 pairs of black full siblings and 106 half-sibling pairs (National Longitudinal Survey of Youth). Results support a common heritage view of the growth of academic knowledge. (SLD)

Whether genetic and environmental effects on academic achievement changed as a function of the quality of children's environment was studied with 1664 pairs of full siblings, 366 pairs of half siblings, and 752 pairs of cousins. Little evidence was found of genotype-environment interactions. (SLD)

Studied continuity and change in general cognitive ability from infancy to adolescence in adoptees (107 children), biological siblings (87 pairs), and twins (224 monozygotic and 189 dyzygotic pairs). Findings generally support previous findings about genetic and environmental factors, with the exception that in the transition to adolescence,…