Identification of a group of children with dyslexia by means of IQ-achievement discrepancies.

The reading and spelling abilities of 462 school children of mean age 8 years 7 months were examined in relation to their intellectual abilities (as assessed by the WISC-R) by means of cluster analysis. The analysis identified five groups. In one group reading and spelling were considerably poorer than their intellectual abilities. The performance of the five groups was examined on a number of cognitive tests commonly associated with dyslexia. The group identified as having significant discrepancies showed the poorest performance on many of these tests. In addition this group showed other features associated with dyslexia. Further analysis indicated the existence of two subgroups which differed significantly in performance on the cognitive tests.