Floyd, Shands, Rafael, Bergeron and McGrew (2009) used generalizability theory to test the reliability of general-factor loadings and to compare three different sources of error in them: the test battery size, the test battery composition, the factor-extraction technique, and their interactions. They found that their general-factor loadings were…

In a recent paper, Johnson, Bouchard, Krueger, McGue, and Gottesman (2004) addressed a long-standing debate in psychology by demonstrating that the g factors derived from three test batteries administered to a single group of individuals were completely correlated. This finding provided evidence for the existence of a unitary higher-level general…

Fluctuating asymmetry (FA) is the non-pathological left-right asymmetry of body traits that are usually left-right symmetrical, such as eye breadths and elbow to wrist lengths in humans, but which can be affected by developmental stressors. It is generally considered throughout biology to be an indicator of developmental instability and thus of…

Taylor (1980) claims to show that the similarity in IQ between monozygotic twins reared apart found in prior studies is due to similarity in their environments. A reanalysis using Taylor's classification of environments but an alternative IQ measure shows that his findings do not constructively replicate. (Author/RD)

In two recent papers, Johnson & Bouchard [Johnson, W., & Bouchard, T. J., Jr. (2005a). The structure of human intelligence: It is verbal, perceptual, and image rotation (VPR) , not fluid and crystallized. "Intelligence," 33, 393-416, Johnson W., & Bouchard, T. J., Jr. (2005b). Constructive replication of the visual…

The concept of a general intelligence factor or "g" is controversial in psychology. Although the controversy swirls at many levels, one of the most important involves "g's" identification and measurement in a group of individuals. If "g" is actually predictive of a range of intellectual performances, the factor…

Recent work with the 42 mental ability tests administered to participants of the Minnesota Study of Twins Reared Apart (MISTRA) has suggested that there are important dimensions of mental ability that function independently of "g". Two of these dimensions, rotation-verbal and focus-diffusion, appear to involve trade-offs: greater…

A battery of "g" loaded mental ability tests was administered to 274 Bedouin children and adolescents, full and half siblings from 106 families. Results demonstrate internal validity for the tests in this cultural context and support the idea that shared family environment is a strong determinant of sibling similarity for children in the…

Empirical data suggest that there is at most a very small sex difference in general mental ability, but men clearly perform better on visuospatial tasks while women clearly perform better on tests of verbal usage and perceptual speed. In this study, we integrated these overall findings with predictions based on the Verbal-Perceptual-Rotation (VPR)…

Provides a comprehensive contemporary summary of the world literature on IQ correlations between relatives. A profile of average correlations consistent with a polygenic mode of inheritence is revealed from a summary of 111 studies, although a marked degree of heterogeneity of the correlations within familial groupings is also found. (CS)

Reviews the work of Arthur Jensen, noting his extensive bibliography and characterizing his work as an extension of the British Biological-Theoretical Tradition. Proposes a new definition of "Jensenism" based on the Jansenist heresy. (SLD)

Described is an ongoing study of monozygotic and dizygotic twins, separated in infancy and reared apart. Discussed are the procedures and results of this study with interpretations of the results. The effects of parenting, education, and other interventions are considered. (CW)