Authors: Wagner, R. K., Zirps, F. A., Edwards, A. A., Wood, S. G., Joyner, R. E., Becker, B. J., Liu, G., & Beal, B..
Publication: Journal of Learning Disabilities (Sage Journals). First Published Online May 26, 2020 2020 | DOI: 10.1177/0022219420920377
How prevalent is dyslexia? A definitive answer to this question has been elusive because of the continuous distribution of reading performance and predictors of dyslexia and because of the heterogeneous nature of samples of poor readers. Samples of poor readers are a mixture of individuals whose reading is consistent with or expected based on their performance in other academic areas and in language, and individuals with dyslexia whose reading is not consistent with or expected based on their other performances. In the present article, we replicate and extend a new approach for determining the prevalence of dyslexia. Using model-based meta-analysis and simulation, three main results were found. First, the prevalence of dyslexia is better represented as a distribution that varies as a function of severity as opposed to any single-point estimate. Second, samples of poor readers will contain more expected poor readers than unexpected or dyslexic readers. Third, individuals with dyslexia can be found across the reading spectrum as opposed to only at the lower tail of reading performance. These results have implications for screening and identification, and for recruiting participants for scientific studies of dyslexia.
Wagner, R. K., Zirps, F. A., Edwards, A. A., Wood, S. G., Joyner, R. E., Becker, B. J., Liu, G., & Beal, B. (2020). The Prevalence of Dyslexia: A New Approach to Its Estimation. Journal of Learning Disabilities, 53(5), 354–365. https://doi.org/10.1177/0022219420920377
Excerpts from “General Discussion” section of full text:
These results have implications for sample selection in scientific studies of dyslexia. Recruitment should target individuals whose reading is poor relative to their level of oral language instead of recruiting on the basis of poor reading relative to age or grade peers. They also have implications for screening for dyslexia. Approaches that rely on absolute rather than relative poor performance on predictors of reading, rudimentary aspects of reading such as letter knowledge, or reading itself will likely miss more individuals with dyslexia than it will correctly identify, and the majority of individuals identified will likely be expected rather than unexpected poor readers.
One issue that arises is that the conclusion that individuals with dyslexia occur throughout the reading spectrum is at odds with policy and practices that limit identification to individuals who are substantially behind their peers or state standards. We argue that science should inform public policy and practice rather than using public policy and practice to inform science. In the past, the definition of specific learning disability included the requirement that IQ needed to be equal or greater than 90. We now recognize that specific learning disabilities including dyslexia can occur throughout the range of cognitive and language abilities, which includes both lower than average and higher than average levels of functioning. Whether individuals with dyslexia whose level of reading performance is average or better than average relative to their peers should be eligible for special education services is an issue that reflects political and economic considerations in addition to scientific ones. At the very least, individuals with dyslexia and their families should know about their condition regardless of whether they are eligible for special education services at the present time. They might have better educational and occupational outcomes with access to accommodations and assistive technology such as text-to-speech ….