Estimating incidence of developmental dyslexia in Hong Kong: What differences do different criteria make?

Based on the data of a school-referred sample of Cantonese-speaking Chinese children who met the Hong Kong criterion of dyslexia, we estimated for developmental dyslexia of Chinese children aged between 6 and 10 in Hong Kong an incidence rate of 0.66% and a gender ratio of 3.29 boys to 1 girl over a four-year period. We also explored the differences in estimates based on this Hong Kong criterion that emphasizes cognitive markers with more conventional discrepancy-based criteria. In view of the possible biases in self-selection and underreporting in the data of the school-referred sample, we compared the figures with those derived from the sample of the normative study of the Hong Kong Test of Specific Learning Difficulties in Reading and Writing, which yielded an estimate of 9.7% in prevalence rate and boy-girl gender ratio of 2 to 1 over a one-year period. The differences in estimates based on the two samples and implications of the findings are discussed in light of the limitations of the study. Copyright © 2008 Taylor & Francis Group, an informa business.