COVARIATION AMONG MEASURES OF COGNITIVE-ABILITY AND ACADEMIC-ACHIEVEMENT IN THE COLORADO-ADOPTION-PROJECT - SIBLING ANALYSIS

Although correlations among measures of cognitive ability and academic achievement are substantial, relatively little is known about the eti ology of their interrelationships. The purpose of the current study wa s to assess the etiology of these relationships by applying the method s of multivariate behavioral genetic analysis to sibling data from the Colorado Adoption Project. The current study analyzed data from 100 p airs of related siblings and 90 pairs of unrelated siblings tested at age 7 on two measures of cognitive ability (verbal comprehension and p erceptual organization) and two measures of academic achievement (read ing recognition and mathematics achievement). Phenotypic correlations among the cognitive and achievement measures averaged about 0.30. Alth ough a substantial proportion of the covariation among the measures wa s due to influences shared with verbal ability, results of fitting a C holesky factor model to the data provided evidence for significant cov ariation between the achievement measures that was independent of cogn itive ability. Results of the genetic analysis confirmed previous find ings of substantial genetic influence, with heritabilities ranging fro m 0.21 for mathematics achievement to 0.60 for perceptual organization . The environmental variance was primarily due to nonshared influences specific to each of the measures, with shared environmental influence s being nonsignificant. In addition, genetic influences accounted for most of the phenotypic covariance among the variables, with much of th e genetic covariation being due to influences shared with verbal abili ty.