Dyslexia is also known as reading disorder. It is a learning disability characterized by reading trouble and despite normal intelligence. Different people are affected to varying degrees. Problems may include difficulties in spelling words, reading quickly, writing words, "sounding out" words in the head, pronouncing words when reading aloud and understanding what one reads. Often these difficulties are first noticed at school. The percentage of people with dyslexia is unknown, but it has been estimated to be as low as 5% and as high as 17% of the population. While it is diagnosed more often in males,some believe that it affects males and females equally.
There are different definitions of dyslexia used throughout the world, but despite significant differences in writing systems, dyslexia occurs in different populations. Dyslexia is not limited to difficulty in converting letters to sounds, and Chinese dyslexics may have difficulty converting Chinese characters into their meanings. The Chinese vocabulary uses logographic, monographic, non-alphabet writing where one character can represent an individual phoneme.
The phonological-processing hypothesis attempts to explain why dyslexia occurs in a wide variety of languages. Furthermore, the relationship between phonological capacity and reading appears to be influenced by orthography Dyslexia and attention deficit hyperactivity disorder (ADHD) commonly occur together, about 15% of people with dyslexia also have ADHD and 35% of those with ADHD have dyslexia.