Analysis of standardized achievement tests by classical test theory and genetic factor analysis models

The purpose of this study was to analyze standardized achievement test scor es of twin and non-twin pupils. These scores were analyzed by genetic facto r analysis in consideration of classical test theory. Samples were 953 pupi ls; 100 monozygotic (MZ) twin pairs, 25 dizygotic (DZ) twin pairs, and 703 non-twins. On the basis of results by Toyoda & Muraishi (1998), non-twins' scores were used for stabilizing covariance structure. Four subjects (Japan ese, social studies, mathematics, and science) were analyzed through the mo del. Evidence of (i) genetic influences, (ii) common environment, and (iii) non-shared environment showed that large differences existed in the struct ure of achievements on four subjects. The ratios of variances for achieveme nt of Japanese were as follows : (i) 0.0%, (ii)64.5%, (iii) 2.9%; those of social studies were (i) 52.3%, (ii) 17.0%, (iii) 4.7%; those of mathematics were (i) 0.0%, (ii) 47.7%, (iii) 10.4%, while those of science were (i) 56 .1%, (ii) 0.0%, (iii) 13.3%, respectively. Comparing fitness among various models of classical test theory showed the best fit for congeneric measurem ent. It warns us against the use of the alpha-coefficient that assumes tau- equivalent measurement in calculating coefficient of reliability.