Toward a definition of dyslexia

A precise and inclusionary definition of dyslexia is sorely needed for at least three reasons. First, accurate identification of dyslexia requires that the key symptoms and characteristics be specified. Second, treatment of dyslexia, including early intervention and general teaching methods, must be based on an informed understanding of what difficulties impede reading develop ment and reading mastery for children and adults with reading disabilities. Third, an operational definition is essential for research purposes. More specifically, to investigate the causes and consequences of dyslexia, to examine whether there are different types of reading problems, and to explore how dys lexia relates to other disorders, it is crucial to study individuals who meet well-specified selection criteria. A number of recent papers and books address, in detail, this need for an opera tional and inclusionary definition of dyslexia and are recom mended for those who wish to pursue more in-depth reviews of the definitional issues in dyslexia (Fletcher and Morris 1986; Lyon and Moats 1993; Lyon et al. 1993; Morris 1988, 1993; Morris, Lyon, Alexander et al. 1994; Shaywitz, Shaywitz, Liberman et al. 1991).

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