The general ability index of the WISC-IV. [L’indice di abilità generale della scala WISC-IV].

The General Ability Index (GAI) of the intelligence scale WISC-IV is a score obtained adding the scores for indices of Verbal Comprehension and Visual-Perception Reasoning. We aim to show the calculation of GAI for the Italian standardization sample and its psychometric properties. We provide the tables for the computation of the differences between IQ and GAI, with the cumulative percentages of the differences for the total sample and for 7 subgroups of subjects divided according to the GAI score obtained; the aim is that of providing data of infrequent differences needed for clinical screening. In the conclusions we offer a brief discussion of the clinical utility of the Index GAI.