A Taxometric Investigation of Developmental Dyslexia Subtypes

Long-standing issues with the conceptualization, identification and subtyping of developmental dyslexia persist. This study takes an alternative approach to examine the heterogeneity of developmental dyslexia using taxometric classification techniques. These methods were used with a large sample of 671 children ages 6-8who were diagnosedwith severe reading disorders. Latent characteristics of the sample are assessed in regard to posited subtypes with phonological deficits and naming speed deficits, thus extending prior work by addressing whether these deficits embody separate classes of individuals. Findings support separate taxa of dyslexia with and without phonological deficits. Different latent structure for naming speed deficits was found depending on the definitional criterion used to define dyslexia. Nonphonologically based forms of dyslexia showed particular difficulty with naming speed and reading fluency. Copyright (C) 2011 John Wiley & Sons, Ltd. Practitioner Points: Support for separate subtypes of dyslexia, with and without phonological deficits (PDs), indicates a need for different approaches to intervention. A discrepancy-based criterion identifies more non-PD cases that may be missed with a response-to-intervention diagnosis. Sound symbol correspondence and decoding measures may best distinguish cases of dyslexia with and without PDs.