Here we take a look at different writing systems and if they influence the development of dyslexia. Given the various language writing system, as well as orthographic depth, one can expect variances in popularity rates. Back in the 80’s when systematic cross-linguistic comparisons were introduced for the first time, dyslexia was surprisingly higher than what had been previously believed, not only in the US but also in countries such as Japan and China (Stevenson et al., 1982). In the past two decades research has indicated that in Japanese speakers, the popularity rate has been generally lower than the typical English rate of 5 to 10%. As Japanese readers were studied using the syllabic Kana writing system, the popularity was estimated to be 2 to 3% - partly because of the shallow orthography and transparent grapheme-sound correspondence. By comparison, the readers were assessed using the logographic system, Kanji, the popularity was 5 to 6% (Wydell, 2012). Also, the popularity of Chinese speakers is around 3.9% (Sun et al., 2013). This rate is similar to the popularity of dyslexia in orthographically shallow languages (e.g., 3.1 to 3.2% for Italian: Barbiero et al., 2012).
There is no biological test for the diagnosis of dyslexia. The very meaning of dyslexia is based primarily on reading performance and testing. The popularity is highly responsive to the basis used for the diagnosis of dyslexia. In a large study of German children, popularity was between 1.9 to 2.6% when the basis was used for a reading score of 1.5 to 1 standard deviations below the normal and average performance in at least one other cognitive measure (Moll, Kunze, Neuhof, Bruder, & Schulte-Korne, 2014). This is consistent with the theory that the popularity rate is lower for orthographically shallow languages, as previously mentioned. The German popularity rate jumps up a range of 7.1 t 15.6%. Though, if you’re only reading the score of 1.5 to 1 standard deviations below the norm are used.
Positioned on the current benchmark of reading performance, the popularity rate of dyslexia in this orthographically shallow language (German) as high a rate for a language with deep orthography (e.g., English). This is a significant difference, so a more biological evidenced-based set of recognition benchmark for diagnosis of dyslexia is highly desirable (Tanaka et al., 2011).
More and more, we’re seeing research on popularity rates that suggest that dyslexia exists in all languages at a more pronounced rate than what was originally assessed. The popularity rate varies with orthographic depth, with a higher popularity rate, which requires further research.
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