No differential heritability of intelligence test scores across ability levels in Norway

The possibility of differential heritability of intelligence test scores across levels of ability has been raised in several recent reports. In the present paper intelligence test data from 862 monozygotic and 1325 dizygotic male twin pairs tested at about 19 years of age were analyzed in search for changes in heritability and shared environmentality as a function of ability level. The analyses were performed by means of multiple regression models (e.g., Cherny et al., 1992). No evidence of differential heritability across different ability levels was detected.