An individual diagnosed with dyslexia in childhood typically remains dyslexic throughout his/her life. However, the cognitive profile of adults with dyslexia has been less explored than that of children. This meta-analytic study is intended to clarify three questions: (1) To what extent, and in what manner, do adults with reading difficulties (dyslexia) differ from typical adult readers in measures of reading and writing competence and related cognitive skills?; (2) To what extent do speed measures pose a greater challenge than accuracy measures in an adult population that has already had years of print exposure?; and (3) To what extent does orthographic transparency modulate the reading profile of adults with dyslexia? A total of 178 studies comparing adults with dyslexia and matched controls were reviewed. The results showed that adults with dyslexia exhibited poor performance on almost all reading and writing tasks expressed by very large effect sizes (range 1.735 ≤ d ≤ 2.034), except for reading comprehension (d = 0.729). Deficits in reading- and writing-related variables are also present but with a lower expression (range 0.591 ≤ d ≤ 1.295). These difficulties are exacerbated for speed measures, especially for word and pseudoword reading, phonological awareness and orthographic knowledge. Orthographic transparency proved to be a significant moderator of dyslexic deficits in word and pseudoword reading, reading comprehension, spelling and phonological awareness, with the expression of the deficits being weaker on transparent-as opposed to intermediate and opaque-orthographies. Overall, the meta-analysis shows that reading and writing difficulties persist in adulthood and are more pronounced in speed measures. Moreover, symptoms are more severe for reading and writing than they are for measures tapping into the cognitive processes underlying reading skills. Orthographic transparency has a significant effect on the manifestation of dyslexia, with dyslexia symptoms being less marked on transparent orthographies. In addition, phonological awareness seems to be a minor problem in adulthood, especially for transparent orthographies.
Keywords: Dyslexic adults; Meta-analysis; Orthographic transparency; Phonological awareness; Reading; Spelling.