ABSTRACT
Specific reading disability, or developmental dyslexia, has been defined as “a disorder manifested by difficulty in learning to read despite conventional instruction, adequate intelligence, and socio-cultural opportunity. It is dependent upon fundamental cognitive abilities which are frequently constitutional in origin” (Critchley, 1970, p. 5). This definition has led to diagnosing dyslexia on the basis of the discrepancy between a subject’s IQ scores and his or her reading achievement scores. However, diagnosing reading disability on the basis of an IQ-achievement discrepancy has been criticized for several reasons. The validity of the assumptions that underlies the use of IQ scores in defining reading disabilities has been questioned (Siegel, 1989). For instance, IQ scores are not able to account for more than 20% to 25% of variance seen in reading performance, particularly in young children. Stanovich, Cunningham, and Feeman (1984) reviewed studies of the relationship between reading achievement and IQ scores at different grade levels, and although the correlation coefficients were around 0.6 and 0.7 for children aged 14 and above, the coefficients were around 0.4 for the first three grades. A more serious but pragmatic problem is that diagnosis based on IQ scores does not lead to recommendations regarding remediation, instruction, and management of reading problems. For these reasons it has been argued that defining reading disabilities on the basis of a discrepancy between IQ and achievement is untenable (e.g., Joshi, 1995; Joshi & Leong, 1993; Stanovich, 1991).
