School Achievement, Intelligence, and Personality in Twins

Abstract

A sample of 47 MZ and 49 DZ pairs of Brazilian twins was investigated in relation to school achievement in six specific areas of study, as well as performance in the test of Dominoes, the Differential Aptitude Tests (DAT) and Griéger's Characterological Questionnaire. Significant F-ratios (variance within DZ/variance within MZ) were observed for the school grades obtained in five of the six areas considered, as well as for their general average; the same being true for the results on the indicated measure of general intelligence, six of the eight DAT tests, and two of the characterological elements. There is a clear positive relationship between the grades earned by the twins and their performance in the Dominoes test. Achievement in Portuguese and foreign language correlates positively with DAT's Sentences; and achievement in mathematics correlates positively with DAT's Numerical Ability, Abstract Reasoning, and Clerical Speed and Accuracy. The results show an agreement with previous estimates of the genetic determination of these variables, which is to a certain extent surprising if we consider the differences in sample sizes, age, and degree of schooling of the subjects, environmental differences, and the dissimilarities which exist between the homes and school systems of USA, Europe, and Brazil.