A Longitudinal Factor Model For Studying Change In Ability Structure

Models of the Longitudinal Factor Analysis type were designed to describe the development of ability structure between the ages 10 and 13. The parameters of the models were estimated by the LISREL program (Jöreskog & van Thillo, 1973). The sample comprised 375 girls and 353 boys who were tested at age 10 and retested at age 13 with six ability tests and two achievement tests. The results indicate that verbal, inductive, and spatial abilities can be described as developing fairly independently of each other between the ages 10 and 13. At age 13, but not at age 10, two subfactors of the inductive factor could be differentiated. The unique variances show a marked decrease between age 10 and age 13. Consequently the factors, and the relationships between factors, explain more of the variance of the response variates at age 13 than at age 10.