Intellectual Status and Intellectual Growth

Abstract

Studying growth in ability is made difficult by (a) unreliability of measures, (b) inequality of units in which measures are expressed, and (c) nonequivalence in what is measured by different instruments and at different levels. These problems are illustrated in analyses of Harvard Growth Study data, where 2 intelligence tests were given to each of 593 pupils each yr. for 6 yrs. The maximum reliability of intellectual growth appears to be about .25 or .30. An unbiased estimate of the obtained correlation of status with gain appears about .10, but this correlation has apparently been reduced by inequalities in the units of measure between (and within) instruments, and by the fact that different tests measure somewhat different functions.

This paper was presented in a slightly different version as a presidential address before the American Psychological Association Division of Educational Psychology (Division 15), Chicago, 1965.