Reading and reading-related skills in adults with dyslexia from different orthographic systems: a review and meta-analysis

While developmental dyslexia is known to persist from childhood into adulthood, the precise cognitive and linguistic profile of adult dyslexic readers remains less understood than that of children. Prior research has largely concentrated on English speakers, leaving questions about how adults across different writing systems manage lifelong reading difficulties. This meta-analytic study addresses three fundamental questions: To what extent and in what manner do adults with dyslexia differ from typical readers in reading, writing, and related cognitive skills? Do speed measures pose a greater challenge than accuracy measures in adults with years of print exposure? And how does orthographic transparency modulate the adult reading profile?

The authors conducted a systematic review and meta-analysis of studies published between 2006 and 2019, identifying 178 studies that compared adults with dyslexia to matched control groups. These studies encompassed 1,817 effect sizes across diverse linguistic backgrounds. The included samples were categorized by orthographic transparency into transparent, intermediate, and opaque systems. Extracted measures were grouped into reading and writing variables, reading- and writing-related cognitive variables, and general cognitive variables. Furthermore, tasks were coded by whether they measured response accuracy or processing speed.

The results reveal that reading and writing difficulties persist into adulthood, with adults with dyslexia performing poorly across almost all literacy tasks, yielding very large effect sizes. These deficits are notably more severe in speed measures—such as word and pseudoword reading fluency, rapid automatized naming, and orthographic knowledge—than in accuracy measures. Interestingly, reading comprehension showed smaller group differences than single-word decoding tasks. Orthographic transparency emerged as a significant moderator: the expression of dyslexic deficits is notably weaker in transparent orthographies compared to intermediate and opaque ones, demonstrating that writing system consistency shapes the long-term manifestation of dyslexia.