Covariation of mathematics achievement and general cognitive ability in twins

Although the phenotypic relationship between mathematics performance and general cognitive ability has been well established, relatively few studies have attempted to examine the nature of this observed relationship. The purpose of the present report was to assess the etiology of the covariation between mathematics performance and general cognitive ability in data from a sample of 555 twins selected for learning deficits (310 monozygotic [MZ] and 245 same-sex dizygotic [DZ] twin pairs) and from a sample of 570 control twin pairs (319 MZ and 251 same-sex DZ twins). Subtests of the Wide Range Achievement Test and the Peabody Individual Achievement Test were used as measures of mathematics performance, whereas the verbal IQ and performance IQ scores from the Wechsler Intelligence Scale for Children-Revised or Wechsler Adult Intelligence Scale-Revised were used as measures of general cognitive ability. In both samples, results of fitting bivariate genetic structural equation models to the data indicated that approximately 90% of the variability in a latent factor for math performance and 80% of that from general cognitive ability were due to genetic effects. In addition, almost 90% of the phenotypic correlation between math performance and general cognitive ability was due to heritable influences in both samples. Thus, the phenotypic relationship between mathematics performance and general cognitive ability latent factors is due primarily to genetic influences. (C) 2000 Society for the Study of School Psychology. Published by Elsevier Science Ltd.