In the same ITBS data, schools’ average scores in reading correlated 0.88 with their average scores in mathematics (Table 9.2), indicating that knowing schools’ average scores in one of these two subjects allows one to predict more than three-fourths of the variation in school means in the second subject. As a consequence, one typically finds only small differences in the correlations between related and unrelated subjects, which makes the use of this convergent and discriminant evidence difficult.
