A study applied the polygenic threshold model to previously reported differences in gender ratios among children with reading disabilities and close family members with similar disabilities. The results were found to be predictable with the model. (MSE)

Identifies three main strengths of Casey's spatial ability model, but notes that a study by McKeever found different results concerning the relationship between familial handedness and females' mental rotation ability. Considers the use of a familial handedness measure to be a weakness of the model because handedness might not be an inherited…

Notes Halpern's general support for Casey's model. Addresses differences in Casey's and McKeever's findings on familial handedness and females' spatial ability by performing another experiment in which data are analyzed according to two different theoretical assumptions. Addresses the question of the heritability of handedness by noting that what…

This study analyzed the Tertiary Admission Examination and Australian Scholastic Aptitude Test results for 264 pairs of 17-year-old monozygotic and dizygotic twins in Western Australia to determine if examination performance is influenced by environmental or genetic factors. Purely environmental models are rejected as inadequate explanations of…