How well is psychometric g indexed by global composites? Evidence from three popular intelligence tests.

Global composites (e.g., IQs) calculated in intelligence tests are interpreted as indexes of the general factor of intelligence, or psychometric g. It is therefore important to understand the proportion of variance in those global composites that is explained by g. In this study, we calculated this value, referred to as hierarchical omega, using large-scale, nationally representative norming sample data from 3 popular individually administered tests of intelligence for children and adolescents. We also calculated the proportion of variance explained in the global composites by g and the group factors, referred to as omega total, or composite reliability, for comparison purposes. Within each battery, g was measured equally well. Using total sample data, we found that 82%-83% of the total test score variance was explained by g. The group factors were also measured in the global composites, with both g and group factors explaining 89%-91% of the total test score variance for the total samples. Global composites are primarily indexes of g, but the group factors, as a whole, also explain a meaningful amount of variance.