Research note: a learning disability index (LDI) derived from the WISC-R: age differences in referred children.

A learning disability index (LDI) based on a principal components analysis of the WISC-R normative data has been developed to depict verbal or nonverbal deficits on that test. This index was calculated for the individual test performance of a total of 1371 children referred to a school-board psychology service because of educational difficulties. These children, categorised by sex and age, returned mean scores on this index that were reliably different from the scores of the normative population only after the age of 8 years in the case of the boys, and 7 years in the girls. This cross-sectional age effect was confirmed by longitudinal data obtained from the test-retest scores of a subset of these children.