TABLE 1.

Selected definitions of dyslexia.

Year	Definition	Organization	Source
1968	[Dyslexia is] a disorder manifested by difficulty in learning to read despite conventional instruction, adequate intelligence and sociocultural opportunity. It is dependent upon fundamental cognitive disabilities which are frequently of constitutional origin	World Federation of Neurology	Critchley (1970), as cited in Snowling (2000, p. 15)
1994	Dyslexia is one of several distinct learning disabilities. It is a specific language-based disorder of constitutional origin characterized by difficulties in single word decoding, usually reflecting insufficient phonological processing abilities. These difficulties in single-word decoding are often unexpected in relation to age or other cognitive abilities; they are not the result of generalized developmental disability or sensory impairment. Dyslexia is manifested by a variable difficulty with different forms of language, including, in addition to a problem with reading, a conspicuous problem with acquiring proficiency in writing and spelling	Orton Dyslexia Society (now called the International Dyslexia Association)	Snowling (2000, pp. 24–25)
2002	Dyslexia is a specific learning disability that is neurobiological in origin. It is characterized by difficulties with accurate and/or fluent word recognition and by poor spelling and decoding abilities. These difficulties typically result from a deficit in the phonological component of language that is often unexpected in relation to other cognitive abilities and the provision of effective classroom instruction. Secondary consequences may include problems in reading comprehension and reduced reading experience that can impede growth of vocabulary and background knowledge	International Dyslexia Association	https://dyslexiaida.org/definition-of-dyslexia/ (downloaded March 2018)
2009	Dyslexia is a learning difficulty that primarily affects the skills involved in accurate and fluent word reading and spelling	British Dyslexia Association	https://www.bdadyslexia.org.uk/news/definition-of-dyslexia (downloaded December 2019)
	Characteristic features of dyslexia are difficulties in phonological awareness, verbal memory and verbal processing speed
	Dyslexia occurs across the range of intellectual abilities
	It is best thought of as a continuum, not a distinct category, and there are no clear cut-off points
	Co-occurring difficulties may be seen in aspects of language, motor co-ordination, mental calculation, concentration and personal organization, but these are not, by themselves, markers of dyslexia
	A good indication of the severity and persistence of dyslexic difficulties can be gained by examining how the individual responds or has responded to well founded intervention
2017	[Dyslexia is] a persistent and unexpected difficulty in developing age- and experience-appropriate word reading skills	N/A	Parrila and Protopapas (2017)