Impact of Cut-off Points on Classification and Cognitive Profiles of Reading Difficulties

Reading difficulties are prevalent globally, with the simple view of reading (SVR) categorizing struggling readers into three groups: dyslexia (decoding difficulties), specific comprehension difficulty (SCD, language comprehension difficulties), and mixed difficulty (both). The proportion of children in these groups can be influenced by various factors, including the cut-off points used to define reading difficulties. This study aimed to explore whether the distribution of children across these SVR-predicted groups varies at different levels of reading comprehension difficulty and if the cognitive profiles within these groups remain consistent across these levels. Previous research suggests a potential shift in the relative importance of decoding and language comprehension with age, where decoding is more critical for younger readers and language comprehension for older readers, influencing group proportions over time.

The study reanalyzed data from 209 New Zealand primary school children (Years 4–6, aged 8–10 years) identified as having reading comprehension difficulties. Participants were initially screened for reading difficulties using school-based assessments and then confirmed using the WJIV Passage Comprehension test (below 40th percentile). A two-step cluster analysis was used to assign children to dyslexia, SCD, or mixed difficulty groups. Researchers examined the distribution of children across these groups at eight different levels of reading comprehension difficulty and analyzed their strengths and weaknesses profiles across 14 reading-related tests at four levels of reading ability.

The study found that the proportion of children in each group varied significantly based on the level of reading comprehension difficulty. Children with more severe reading comprehension difficulties were more likely to exhibit a mixed difficulty profile (both decoding and language comprehension issues) compared to SCD or dyslexia profiles. Importantly, dyslexia, SCD, and mixed difficulty profiles were identifiable at all levels of reading comprehension difficulty. However, the severity of weaknesses in reading-related skills increased as reading comprehension difficulties became more pronounced. The cognitive profiles of these groups remained largely distinct even at different levels of reading impairment, although subtle differences, particularly in phonological skills, were observed.

The findings suggest that struggling readers demonstrate distinct cognitive profiles across all levels of reading ability. This has significant implications for identifying and supporting these readers. Children with the most severe reading comprehension difficulties may require intensive interventions targeting both decoding and language comprehension. Conversely, those with less severe difficulties might benefit from programs tailored to address specific weaknesses in either decoding or language comprehension. The study highlights the need for nuanced approaches to intervention based on the specific cognitive profile and severity of reading impairment, and its relevance to tiered models of reading support is discussed.