Novel reading index for identifying disordered reading skill development: A preliminary study

Children with ADHD are at high risk of developing a Reading Disability (RD), although the reasons remain unclear. ADHD-associated impairments, including processing speed, can complicate clinical evaluation for a co-occurring RD diagnosis. We propose a novel metric to (a) assess reading development and (b) provide an alternative method to classifying readers that may aid investigations for etiologies of RD in ADHD. Specifically, as both phonological decoding and word recognition skills are important precursors of reading fluency, we propose a new quantitative method comparing these skills after accounting for variations in perception, motor response, or processing speeds. Forty boys (14 control, 15 ADHD, 11 ADHD/+RD) completed a lexical decision task testing decoding and another assessing word recognition. Response time data was modeled using a Drift Diffusion approach to estimate the underlying reading skills. Using these reading skill estimates, we calculated a novel Reading Tendency Index and classified participants into three reading groups (Decoders, Balanced Readers, and Sight Readers). The reading and cognitive performance of these groups were consistent with theoretical predictions and subsequently provided external validity for the novel Reading Tendency Index classification. Our findings demonstrate a potential classification tool for readers based on individual's developed, reading tendencies.