Validation of a Clinical Method for the Diagnosis of Two Subtypes of Dyslexia

Children with dyslexia were identified and subtyped by two testing methods, word attack and analysis of spelling errors. A phonologically impaired group (n = 54) and an orthographically impaired group (n = 20) were selected from a mid-elementary-school-level referred population for an intervention program. The subtype diagnostic methods were validated by a double dissociation between the groups on a variety of independent measures of phonological and orthographic processing. Phonologically impaired children with dyslexia showed poorer higher-order phonics processing skills, such as sound integration, than did orthographically impaired children with dyslexia. The groups did not differ on lower-order phonics processing skills, such as rhyming or segmentation. Orthographically impaired children showed poorer recognition of nonwords and slower reading speed than did phonologically impaired children. These subtype diagnostic methods can provide clinically important information about dyslexic children's mental processing strengths and weaknesses.