Factor structure of the Italian version of the WAIS-R compared with the American standardization.

Factor analysis for responses to the WAIS-R by 1,630 adults of the Italian standardization sample produced two factor solutions in different age groups, and showed high factorial similarity when compared with the same American solution. An estimate of g factor and variance components showed some difference with American data: a lower proportion of g and common variance, and a greater specificity characterized the Italian version with an almost identical error variance. For both the estimate of g and variance components some change across age groups was observed with g and common variance increasing and specific variance decreasing from youngest to oldest groups.