University of Gothenburg
Child with dyslexia is standing in front of a whiteboard with many letters in elementary school
Photo: Robert Kneschke/

Dyslexia and other reading and writing difficulties

What is dyslexia? What is the rate of occurrence? What are the causes and often associated problems? Jakob Åsberg Johnels provides an explanation.

What is dyslexia?

Well developed reading and writing skills are crucial to a person's ability to function independently in their schoolwork, at their job, or in our modern society in general. As such reading and writing difficulties often constitute a severe disability.

Research conducted over the last decades has clearly shown that reading ability is multidimensional and can initially be divided into a word decoding function on the one hand and a comprehension function on the other. Word decoding refers to the ability to quickly and correctly recognise written words, whereas language comprehension refers to the ability to comprehend the meaning of words/texts, regardless of whether they are written or read aloud.

Based on this model three different types of reading and comprehension problems are defined, each with in some aspects different backgrounds and for which the need for support varies among those affected. One group has problems that are relatively specific to word decoding. This is what we typically refer to when using the term dyslexia, and this group usually also has difficulties spelling. Another group does not have any difficulties in terms of decoding words, but does have difficulties in language comprehension (i.e. specific comprehension problems). A third group manifests both word decoding problems and abnormalities in their language comprehension development. All these types of problems are detrimental to reading comprehension of texts, but, as has been described above, for partially different reasons.


Jakob Åsberg Johnels

Rate of occurrence

There is reason to believe that both dyslexia and comprehension difficulties constitute the lower portion of the standard distribution of reading and writing skills found in the general population. The rate of dyslexia and similar difficulties is therefore partially dependent on one's definition of "abnormal". However, according to the definitions typically used in research studies and clinical contexts, 5-15% of the population has some kind of reading and writing difficulty. It might be the case that (specific) reading comprehension problems are more common than dyslexia


Reading and writing are, at their core, cultural and social skills. For a child to obtain reading and writing skills, continuous practice for several years, as well as support and encouragement from parents and teachers, are usually required. At the same time, research has shown that there is a strong genetic background involved in variation and difficulties in terms of reading and writing skills. Some advances have also been made in the comprehension of the neurobiological background of reading and writing difficulties.

Most research on causes of dyslexia and other reading problems have been conducted on a cognitive analysis level. A number of scientific works have shown that one core problem of dyslexia lies in the person's phonology, i.e. a disorder in terms of comprehending and manipulating language sounds, which in turn might lead the connection between letters and their sounds to become unstable. Several significant works have shown that people with dyslexia can develop their reading if they are made to train their phonological functions.

Other researchers have focused on visuoperceptual difficulties as a cause of dyslexia. Such research has for example been able to establish that people with dyslexia often have a less developed visual sensitivity to movement, and that measuring this ability can provide an indication of a child's reading development. One can expect a strongly increased interest over the coming years in researching the role of visual factors in the development of dyslexia, as well as in how visual and phonological factors interact while the child is learning to read.

Children with specific comprehension problems rarely have any phonological problems. However, other aspects of spoken language – such as vocabulary and syntax – are often poorly developed. Other studies have shown that children with specific comprehension problems may have deficiencies in certain so called executive functions, particularly regarding verbal working memory and planning ability.

Often associated problems

There are a number of other difficulties that tend to be associated with reading and writing difficulties, to name a few:

  • Difficulties in mathematics – both arithmetic and/or mathematic problem solving.
  • ADHD – attention difficulties especially seem to have an adverse effect on word decoding and comprehension.
  • Poor self-confidence and other emotional problems.