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Ann Dyslexia
Ann Dyslexia
Annals of Dyslexia
0736-9387
1934-7243
Springer US New York

38526759
305
10.1007/s11881-024-00305-y
Commentary
Do we really need a new definition of dyslexia? A commentary
Snowling Maggie maggie.snowling@psy.ox.ac.uk

1
Hulme Charles 2
1 grid.4991.5 0000 0004 1936 8948 University of Oxford and St. John’s College, Oxford, England
2 https://ror.org/04v2twj65 grid.7628.b 0000 0001 0726 8331 Oxford Brookes University, Oxford, England
25 3 2024
25 3 2024
2024
74 3 355362
6 3 2024
© The Author(s) 2024
2024
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We provide a commentary on current debates about the definition of dyslexia. We agree with others that dyslexia is best thought of as a dimensional disorder with the best established causal risk factor being a deficit in phonological processing. Dyslexia is particularly common in children from families with a history of dyslexia and in children with preschool language difficulties. We argue that definitions may differ depending upon their purpose. Traditional discrepancy definitions may be useful for research purposes, but when considering the provision of educational services discrepancy definitions are not useful since all children with reading difficulties require reading intervention regardless of their level of IQ.

Keywords

Dyslexia
Definition
Dimensional disorder
Language learning difficulty
issue-copyright-statement© The International Dyslexia Association 2024
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pmcThe nature and definition of dyslexia have been debated ever since it was first identified at the close of the nineteenth century (Kirby & Snowling, 2022). Among the early pioneers, perhaps, it was Samuel Orton’s description of the condition that is closest to current understanding. Although Orton is usually remembered for his attempt to explain the ‘twisting of symbols’ observed in the reading and writing of children with dyslexia, he also documented the familial nature of the disorder, and the tendency for family members to show deficits not necessarily in reading or writing but frequently in speech and language. Here, we will reflect on the points raised by Catts and Petscher and Wolf and colleagues and propose that it is critical for a definition of dyslexia to be evidence-based, and useful in guiding research and practice. Our commentary draws on our longitudinal studies of reading and provides a UK perspective on definitions of dyslexia.

In our view, the broad form of a definition of dyslexia is clear and needs little by way of revision. We believe the core of the definition proposed by the UK Rose Review remains useful and accurate (Rose, 2009).“Dyslexia is a learning difficulty that primarily affects the skills involved in accurate and fluent word reading and spelling. 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”.

The key points here are:

1. Dyslexia is a difficulty in learning to decode/encode print.

2. It is associated with phonological problems.

3. It may occur at different levels of ability.

4. Dyslexia is a dimensional disorder—where we set a cut-off for identification that is to some extent arbitrary.

In addition, Rose noted that an indication of the severity of dyslexia may be provided by how an individual responds to intervention and that dyslexia often co-occurs with other disorders although these are not themselves markers of dyslexia. It is important not to lose sight of these basic facts about dyslexia, but here, we will reflect on some detailed nuances where debates still continue.

Before getting into details about current areas of detailed debate, it is probably worth making three general points.

A dimensional disorder

First, the definition of dyslexia as a dimensional disorder sometimes causes concern. To put it bluntly, if there is no universally accepted cut-off, does this make the disorder less real? We would argue that dimensional disorders are common in medicine: Hypertension (high blood pressure) is a good example. The World Health Organization (WHO) defines hypertension as when “the systolic blood pressure readings on two different days is ≥ 140 mmHg and/or the diastolic blood pressure readings on both days is ≥ 90 mmHg”. Hypertension is a very real problem and can be effectively treated with medications resulting in the prevention of many premature deaths and other medical problems. Dyslexia arguably is the same—it can be detected, and it can be effectively treated, but the cut-off in terms of a reading score needed for a diagnosis is to some extent arbitrary, just as in the case of hypertension. A patient with systolic blood pressure readings on two different days of 139 mmHg is not qualitatively different from a person with systolic blood pressure of 141 mmHg. It is just that 140 mmHg is a boundary above which there is a consensus among many in the medical profession that the advantages of medication outweigh the possible side effects.

Dyslexia and general ability (IQ)

The relevance of measures of general ability (IQ) to the definition of dyslexia continues to be controversial. Early definitions used a discrepancy approach whereby dyslexia was defined as a problem with reading that, from a regression model, was out of line with a person’s age and IQ (for an example, see Rutter & Yule, 1975). Most contemporary definitions have explicitly moved away from a discrepancy definition.

In our view, the way a disorder is defined may vary according to the purposes the definition is to be used for. The Rose Review dealt with the educational policy implications of dyslexia, and for this reason, Rose did not adopt a discrepancy definition. A discrepancy definition might for example deem a child with a reading standard score of 85 and an IQ of 110 as worthy of reading intervention, while a child with a reading standard score of 85 and an IQ of 99 might be deemed not to require intervention. Such a clinical judgement is dubious, as both children have the same level of reading ability and would be likely to benefit from help to improve their reading. Furthermore, there is little evidence that, across a wide range, IQ is predictive of response to reading instruction (Hatcher, 2000; Hatcher & Hulme, 1999; Stuebing et al., 2009).

In contrast to the use of a dyslexia definition to guide treatment, a discrepancy definition may work well in a research context for identifying children with “unexpected” reading problems. Traditionally, many research studies of dyslexia have selected children based on a discrepancy between reading level and age and IQ. There is no doubt that IQ in the general population correlates with reading ability (Rutter & Yule, 1975); hence, using a discrepancy definition in research studies will exclude children whose reading problems are associated with more general learning difficulties (a child with a reading standard score of 85 and an IQ of 85 may be considered to have a less specific difficulty with reading, than a child with the same reading standard score, but an IQ of 110). While it remains unclear the extent to which such selection criteria bias our understanding of the typical characteristics of children with reading problems, it should be noted that individuals of lower measured IQ may well be those with co-occurring conditions, such as developmental language or coordination disorder (Snowling et al., 2020a, 2020b).

Should the causes of a disorder be a part of its definition?

When we talk about the causes of a developmental disorder, we are talking about causal risk factors (Hulme & Snowling, 2009). The development of a disorder typically reflects the interaction of many different causal factors that can be identified at different levels (cognitive, environmental, and biological risk factors). Dyslexia is a highly heritable condition, with the genes involved operating to influence the development of a left hemisphere reading “circuit” involving occipital, temporal, and frontal brain regions. At a cognitive level, the best-established cause of reading problems is a deficit in processing phonological (speech sound) information.

We doubt that these causal risk factors should be made a part of the definition of dyslexia. While we agree that dyslexia has a neurobiological basis, and one of the strongest known risk factors is having a first-degree relative with reading difficulties (Snowling & Melby-Lervåg, 2016) suggesting its origins are likely to be genetic, it is not feasible currently to use biological markers for its identification. Indeed, although numerous genetic variants have been found to be associated with the ‘dyslexia phenotypes’, individual genes have tiny effect sizes accounting for very little variance in reading in the population (Doust et al., 2022). Recent studies that use polygenic risk scores (summing the influence of all identified relevant genes) show that genetic variation accounts for at most 12–16% of the variance in educational attainment (years of education measured in a sample of some 3 million participants; Okbay et al., 2022). Moreover, their effects are not direct and include effects of gene-environment correlation and assortative mating (Meyer et al., 2023 for a review).

Similarly, structural and functional neuroimaging methods, which are costly, do not yet provide information that would be useful in making individual diagnoses of ‘dyslexia liability’. In contrast, measures of cognition and behaviour are psychometrically reliable and of low cost and directly assess the factors that may form the targets of intervention (reading, spelling, and phonological skills). For these reasons, we do not see the rationale for including in a definition of dyslexia a reference to its likely neurobiological causes.

Toward a definition of dyslexia?

The core deficit in phonological processing

The strong relationship between phonological skills and reading and the role of phonological deficits in dyslexia are well known (Melby-Lervåg, Lyster & Hulme, 2012). There is also evidence that phonological deficits are observed in children who go on to be dyslexic prior to reading instruction (Snowling et al., 2019); it has also been shown that phonological skills predict individual differences in reading fluency across alphabetic orthographies (Caravolas et al., 2013). Moreover, while there is relatively strong evidence that phoneme awareness and letter knowledge are causally related to reading problems (e.g. Hulme et al., 2012), rapid improvements in these skills during the first year of formal schooling appear to be strongly predicted by earlier variations in oral language that can be measured in the preschool years (Hulme et al., 2015). Thus, perhaps surprisingly, oral language skills appear to have a direct role in laying the foundations for the development of decoding skills (via effects on the development of phoneme awareness and letter-sound knowledge) as well as being critical for the development of reading comprehension. It seems to us important therefore to acknowledge early oral language difficulties as an important risk factor for dyslexia.

The question remains, however, as to whether our understanding of the causal risk factors for a disorder should be a part of its definition. We believe that it is better not to include claims about causal risk factors in the definition of dyslexia. As referenced above, the WHO definition of hypertension does not reference the numerous causal risk factors operating (genetics, diet, exercise). Similarly, the WHO’s definition of obesity does not mention causal risk factors “obesity … abnormal or excessive fat accumulation that presents a risk to health … a body mass index (BMI) over 30 is obese”.

In our view, there may be advantages in following these examples from medicine and defining dyslexia in terms of what we can easily measure directly at the behavioural level (reading and spelling). While it remains essential to understand the causal risk factors operating in dyslexia, we are not convinced that these should be included in its definition; rather, we would follow other classification systems such as DSM5 (American Psychiatric Association, 2013) and ICD11 (World Health Organisation, 2018), as well as the UK’s Rose (2009) definition and focus on cognitive and behavioural symptoms rather than causal risk factors.

The multifactorial basis of dyslexia

Like many, we have been influenced by the multifactorial model of Pennington and colleagues (Pennington, 2006; McGrath, Petersen & Pennington, 2020). However, there is a danger of going beyond the data when discussing the possible causal risk factors for dyslexia outside of phonology. Wolf et al. propose three such factors: naming speed, executive function, and visual-orthographic skills. We believe that the evidence for rapid-automatized naming (RAN) as a risk factor for the development of reading fluency is relatively strong (e.g. Lervag & Hulme, 2009). However, we do not know of any good evidence that executive function and visual-orthographic skills are causal risk factors. In fact, we would see deficits in orthographic skills as a consequence of a reading problem rather than a cause.

Catts et al. (2024 - this issue) suggest that difficulties in oral language, visual processing, processing speed, and procedural learning are putative causal risk factors for dyslexia. We agree strongly that oral language deficits that predate reading difficulties are a powerful risk factor for both later decoding and reading comprehension problems. However, we contend that the evidence for visual processing having a causal status is lacking, and we have argued elsewhere (as noted by Catts et al., 2024 - this issue) that we find no evidence for a causal role of procedural learning (West et al., 2021). Another sticky point is what is meant by executive function and processing speed and how does the latter differ from naming speed. Both constructs are considered important but are themselves multi-faceted, and there is a lack of direct evidence for their role in learning to read (Malone et al., 2022). Like ‘protective factors’, these are familiar ideas which could be tested empirically but at present might more properly be considered rather speculative hypotheses.

Comorbidity

Related to the multiple deficit view of dyslexia is the issue of comorbidity—the co-occurrence of dyslexia with other disorders. Given that comorbidity is the norm in developmental disorders, it would seem important to note, as did Rose (2009), that dyslexia frequently co-occurs with difficulties in attention, language, mathematics, and motor coordination, but ‘these are not features of dyslexia’ per se. Moreover, until there is further research on the shared risk factors between dyslexia and other disorders, as opposed to specific risk factors, we can only conjecture as to how these affect the progression of dyslexia over time—specifically, are they additive or interactive? (Moll et al., 2020). In a similar vein, dyslexia may lead to low confidence, poor self-esteem, and possibly internalizing or externalizing disorders, but the causal connections are unclear (Donolato et al., 2022). We are on safer ground in stating that poor vocabulary or poor reading comprehension can be a downstream effect of dyslexia, though note, that such difficulties are much less marked than those experienced by children with developmental language disorder (Snowling et al., 2020a, 2020b). We would note a point of disagreement with Catts and Petscher (2022) here. We do not believe that including comorbid disorders in the definition of dyslexia is useful. In fact, we would argue that the failure to recognize clearly that comorbid disorders are distinct from dyslexia has led to confusion in this area. To take a clear example, motor difficulties may be frequently comorbid with dyslexia, but motor problems reflect cognitively distinct mechanisms, and most critically interventions to improve motor skills cannot be expected to reduce reading difficulties as was claimed for example by Dore (Rack et al., 2007; Stephenson & Wheldall, 2008).

Disorder or difference?

A thorny issue is whether dyslexia should be considered a disorder or a disability. This issue is central to the concerns of the neurodiversity movement. In line with the dimensional view, Wolf et al. prefer the notion of a difference. Our views differ from theirs; we prefer to describe dyslexia as a specific learning disorder (affecting the acquisition of reading and spelling skills). While educationists have tended to reject the notion of ‘dyslexia’ as a disorder—believing that this is a medical model of the issues affected individuals face—even medical models of the disease need to determine diagnostic categories if treatment is to be prescribed, as in the case of hypertension discussed earlier. So even though reading skills are normally distributed in the population, we argue that rejection of a category for identification increases the probability that ‘cases’ needing intervention will be missed, and less principled criteria will be used in identification—resources may end up directed to those who obtain private assessments or are from certain social classes or ethnic groups. For similar reasons, we see it as important to prioritize needs based on core characteristics; otherwise, it will be difficult to know how and when to provide intervention. That is not to say that intervention should only be provided for those who fulfil definitional criteria for dyslexia. As our recent Delphi study has shown (Carroll et al., n.d.), there is consensus among experts that many individuals with poor literacy skills deserve to be offered intervention irrespective of whether they fulfil strict diagnostic criteria for ‘dyslexia’.

Conclusions

Although scientific understanding of dyslexia is advanced, its definition continues to be debated. As we have outlined, the core of a definition of dyslexia seems to us to be clear and relatively widely accepted. We have discussed some of the nuances that surround the definition, but these in our view are details rather than fundamental issues. Reading skills in the population are normally distributed, and dyslexia is a term that is used to refer to the bottom end of the distribution (typically between 5 and 10% of the population). We favour using measures of behaviour (reading and spelling skills) as the primary means of diagnosing dyslexia. Although there is a degree of arbitrariness in where the “cut-off” for dyslexia is placed, we do believe that the use of dyslexia as a categorical label is useful both in educational practice and research. The dimensional view clearly entails, however, that such a category may be modified by adjectives—a person might be described as mildly or severely dyslexic depending on their level of literacy needs. It is important in relation to educational policy that it is recognized that reading difficulties are both common and remediable and that suitable interventions are made widely available. Dyslexia is persistent although its effects will differ according to context and the individual differences in related skills that the child brings to the task of learning (see Carroll et al., for a consensus study; Catts & Petscher, 2022). Moreover, there is a good understanding of some of the causal risk factors associated with dyslexia and a significant evidence base of effective interventions for reading and language difficulties. The issues involved in scaling up methods of screening and identification and, following these, providing evidence-based interventions need to be at the forefront of policy and practice (Newbury et al., 2022).

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References

American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders: DSM-5 (Vol. 5, No. 5). American Psychiatric Association.
Caravolas M Lervåg A Defior S Seidlová Málková G Hulme C Different patterns, but equivalent predictors, of growth in reading in consistent and inconsistent orthographies Psychological Science 2013 24 8 1398 1407 10.1177/0956797612473122 23744876
Caravolas, M., Lervåg, A., Defior, S., Seidlová Málková, G., & Hulme, C. (2013). Different patterns, but equivalent predictors, of growth in reading in consistent and inconsistent orthographies. Psychological Science, 24(8), 1398–1407.23744876
Carroll et al., (in preparation) A Delphi Study of Dyslexia.
Catts HW Petscher Y A cumulative risk and resilience model of dyslexia Journal of Learning Disabilities 2022 55 3 171 184 10.1177/00222194211037062 34365842
Catts, H. W., & Petscher, Y. (2022). A cumulative risk and resilience model of dyslexia. Journal of Learning Disabilities, 55(3), 171–184.34365842
Donolato E Cardillo R Mammarella IC Melby-Lervåg M Research review: Language and specific learning disorders in children and their co-occurrence with internalizing and externalizing problems: A systematic review and meta-analysis Journal of Child Psychology and Psychiatry 2022 63 5 507 518 10.1111/jcpp.13536 34747025
Donolato, E., Cardillo, R., Mammarella, I. C., & Melby-Lervåg, M. (2022). Research review: Language and specific learning disorders in children and their co-occurrence with internalizing and externalizing problems: A systematic review and meta-analysis. Journal of Child Psychology and Psychiatry, 63(5), 507–518.34747025
Doust C Fontanillas P Eising E Discovery of 42 genome-wide significant loci associated with dyslexia Nature Genetics 2022 54 1621 1629 10.1038/s41588-022-01192-y 36266505
Doust, C., Fontanillas, P., Eising, E., et al. (2022). Discovery of 42 genome-wide significant loci associated with dyslexia. Nature Genetics, 54, 1621–1629. 10.1038/s41588-022-01192-y36266505
Hatcher PJ Sound links in reading and spelling with discrepancy-defined dyslexics and children with moderate learning difficulties Reading and Writing 2000 13 257 272 10.1023/A:1026486500271
Hatcher, P. J. (2000). Sound links in reading and spelling with discrepancy-defined dyslexics and children with moderate learning difficulties. Reading and Writing, 13, 257–272.
Hatcher PJ Hulme C Phonemes, rhymes, and intelligence as predictors of children’s responsiveness to remedial reading instruction: Evidence from a longitudinal intervention study Journal of Experimental Child Psychology 1999 72 2 130 153 10.1006/jecp.1998.2480 9927526
Hatcher, P. J., & Hulme, C. (1999). Phonemes, rhymes, and intelligence as predictors of children’s responsiveness to remedial reading instruction: Evidence from a longitudinal intervention study. Journal of Experimental Child Psychology, 72(2), 130–153.9927526
Hulme C Snowling MJ Developmental disorders of lanugage 2009 Wiley
Hulme, C., & Snowling, M. J. (2009). Developmental disorders of lanugage. Wiley.
Hulme C Bowyer-Crane C Carroll JM Duff FJ Snowling MJ The causal role of phoneme awareness and letter-sound knowledge in learning to read: Combining intervention studies with mediation analyses Psychological Science 2012 23 6 572 577 10.1177/0956797611435921 22539335
Hulme, C., Bowyer-Crane, C., Carroll, J. M., Duff, F. J., & Snowling, M. J. (2012). The causal role of phoneme awareness and letter-sound knowledge in learning to read: Combining intervention studies with mediation analyses. Psychological Science, 23(6), 572–577.22539335
Hulme C Nash HM Gooch D Lervåg A Snowling MJ The foundations of literacy development in children at familial risk of dyslexia Psychological Science 2015 26 12 1877 1886 10.1177/0956797615603702 26525072
Hulme, C., Nash, H. M., Gooch, D., Lervåg, A., & Snowling, M. J. (2015). The foundations of literacy development in children at familial risk of dyslexia. Psychological Science, 26(12), 1877–1886.26525072
Kirby, P. & Snowling, M. J. (2022). Dyslexia: A history. Montreal: MQUP
Lervåg A Hulme C Rapid automatized naming (RAN) taps a mechanism that places constraints on the development of early reading fluency Psychological Science 2009 20 8 1040 1048 10.1111/j.1467-9280.2009.02405.x 19619178
Lervåg, A., & Hulme, C. (2009). Rapid automatized naming (RAN) taps a mechanism that places constraints on the development of early reading fluency. Psychological Science, 20(8), 1040–1048.19619178
Malone SA Pritchard VE Hulme C Domain-specific skills, but not fine-motor or executive function, predict later arithmetic and reading in children Learning and Individual Differences 2022 95 102141 10.1016/j.lindif.2022.102141
Malone, S. A., Pritchard, V. E., & Hulme, C. (2022). Domain-specific skills, but not fine-motor or executive function, predict later arithmetic and reading in children. Learning and Individual Differences, 95, 102141.
McGrath LM Peterson RL Pennington BF The multiple deficit model: Progress, problems, and prospects Scientific Studies of Reading 2020 24 1 7 13 10.1080/10888438.2019.1706180 32440085
McGrath, L. M., Peterson, R. L., & Pennington, B. F. (2020). The multiple deficit model: Progress, problems, and prospects. Scientific Studies of Reading, 24(1), 7–13.32440085
Melby-Lervåg M Lyster SAH Hulme C Phonological skills and their role in learning to read: A meta-analytic review Psychological Bulletin 2012 138 2 322 10.1037/a0026744 22250824
Melby-Lervåg, M., Lyster, S. A. H., & Hulme, C. (2012). Phonological skills and their role in learning to read: A meta-analytic review. Psychological Bulletin, 138(2), 322.22250824
Meyer MN Appelbaum PS Benjamin DJ Callier SL Comfort N Conley D Parens E Wrestling with social and behavioral genomics: Risks, potential benefits, and ethical responsibility Hastings Center Report 2023 53 S2 S49 10.1002/hast.1477
Meyer, M. N., Appelbaum, P. S., Benjamin, D. J., Callier, S. L., Comfort, N., Conley, D., & Parens, E. (2023). Wrestling with social and behavioral genomics: Risks, potential benefits, and ethical responsibility. Hastings Center Report, 53, S2–S49. 10.1002/hast.1477
Moll K Snowling MJ Hulme C Introduction to the special issue “comorbidities between reading disorders and other developmental disorders” Scientific Studies of Reading 2020 24 1 1 6 10.1080/10888438.2019.1702045
Moll, K., Snowling, M. J., & Hulme, C. (2020). Introduction to the special issue “comorbidities between reading disorders and other developmental disorders.” Scientific Studies of Reading, 24(1), 1–6.
Newbury D Mesa C Puglisi M Nash M Nag S Hulme C Snowling M Challenges for implementation in diverse settings: Reflections on two randomised controlled trials of educational interventions in South American communities Research Papers in Education 2022 38 6 966 986 10.1080/02671522.2022.2065526
Newbury, D., Mesa, C., Puglisi, M., Nash, M., Nag, S., Hulme, C., & Snowling, M. (2022). Challenges for implementation in diverse settings: Reflections on two randomised controlled trials of educational interventions in South American communities. Research Papers in Education, 38(6), 966–986. 10.1080/02671522.2022.2065526
Okbay A Wu Y Wang N Polygenic prediction of educational attainment within and between families from genome-wide association analyses in 3 million individuals Nature Genetics 2022 54 437 449 10.1038/s41588-022-01016-z 35361970
Okbay, A., Wu, Y., Wang, N., et al. (2022). Polygenic prediction of educational attainment within and between families from genome-wide association analyses in 3 million individuals. Nature Genetics, 54, 437–449. 10.1038/s41588-022-01016-z35361970
Pennington BF From single to multiple deficit models of developmental disorders Cognition 2006 101 2 385 413 10.1016/j.cognition.2006.04.008 16844106
Pennington, B. F. (2006). From single to multiple deficit models of developmental disorders. Cognition, 101(2), 385–413.16844106
Rack JP Snowling MJ Hulme C Gibbs S No evidence that an exercise-based treatment programme (DDAT) has specific benefits for children with reading difficulties Dyslexia 2007 13 2 97 104 10.1002/dys.335 17557686
Rack, J. P., Snowling, M. J., Hulme, C., & Gibbs, S. (2007). No evidence that an exercise-based treatment programme (DDAT) has specific benefits for children with reading difficulties. Dyslexia, 13(2), 97–104.17557686
Rose, J. (2009). Identifying and teaching children with dyslexia and other literacy difficulties. https://www.thedyslexia-spldtrust.org.uk/media/downloads/inline/the-rose-report.1294933674.pdf. Accessed 10 Mar 2024.
Rutter M Yule W The concept of specific reading retardation Journal of Child Psychology and Psychiatry 1975 16 3 181 197 10.1111/j.1469-7610.1975.tb01269.x 1158987
Rutter, M., & Yule, W. (1975). The concept of specific reading retardation. Journal of Child Psychology and Psychiatry, 16(3), 181–197.1158987
Snowling MJ Melby-Lervåg M Oral language deficits in familial dyslexia: A meta-analysis and review Psychological Bulletin 2016 142 5 498 10.1037/bul0000037 26727308
Snowling, M. J., & Melby-Lervåg, M. (2016). Oral language deficits in familial dyslexia: A meta-analysis and review. Psychological Bulletin, 142(5), 498.26727308
Snowling MJ Nash HM Gooch DC Hayiou-Thomas ME Hulme C Wellcome Language and Reading Project Team Developmental outcomes for children at high risk of dyslexia and children with developmental language disorder Child Development 2019 90 5 e548 e564 10.1111/cdev.13216 30676649
Snowling, M. J., Nash, H. M., Gooch, D. C., Hayiou-Thomas, M. E., Hulme, C., Wellcome Language and Reading Project Team. (2019). Developmental outcomes for children at high risk of dyslexia and children with developmental language disorder. Child Development, 90(5), e548–e564.30676649
Snowling MJ Hayiou-Thomas ME Nash HM Hulme C Dyslexia and developmental language disorder: Comorbid disorders with distinct effects on reading comprehension Journal of Child Psychology and Psychiatry 2020 61 6 672 680 10.1111/jcpp.13140 31631348
Snowling, M. J., Hayiou-Thomas, M. E., Nash, H. M., & Hulme, C. (2020a). Dyslexia and developmental language disorder: Comorbid disorders with distinct effects on reading comprehension. Journal of Child Psychology and Psychiatry, 61(6), 672–680.31631348
Snowling MJ Hulme C Nation K Defining and understanding dyslexia: Past, present and future Oxford Review of Education 2020 46 4 501 513 10.1080/03054985.2020.1765756 32939103
Snowling, M. J., Hulme, C., & Nation, K. (2020b). Defining and understanding dyslexia: Past, present and future. Oxford Review of Education, 46(4), 501–513.32939103
Stephenson J Wheldall K Miracles take a little longer: Science, commercialisation, cures and the Dore program Australasian Journal of Special Education 2008 32 1 67 82 10.1017/S1030011200025768
Stephenson, J., & Wheldall, K. (2008). Miracles take a little longer: Science, commercialisation, cures and the Dore program. Australasian Journal of Special Education, 32(1), 67–82.
Stuebing KK Barth AE Molfese PJ Weiss B Fletcher JM IQ is not strongly related to response to reading instruction: A meta-analytic interpretation Exceptional Children 2009 76 1 31 51 10.1177/001440290907600102 20224749
Stuebing, K. K., Barth, A. E., Molfese, P. J., Weiss, B., & Fletcher, J. M. (2009). IQ is not strongly related to response to reading instruction: A meta-analytic interpretation. Exceptional Children, 76(1), 31–51. 10.1177/00144029090760010220224749
West G Melby-Lervåg M Hulme C Is a procedural learning deficit a causal risk factor for developmental language disorder or dyslexia? A Meta-Analytic Review. Developmental Psychology 2021 57 5 749 34166019
West, G., Melby-Lervåg, M., & Hulme, C. (2021). Is a procedural learning deficit a causal risk factor for developmental language disorder or dyslexia? A Meta-Analytic Review. Developmental Psychology, 57(5), 749.34166019
World Health Organization. (2018). International classification of diseases (ICD11). https://icd.who.int/en. Accessed 10 Mar 2024.
