Clinical Relevance of NIH Toolbox Cognition Battery Developmental Change in Intellectual and Developmental Disabilities: Associations with Verbal Reasoning

The NIH Toolbox Cognition Battery (NIHTB-CB) assesses crystallized verbal skills,and shows strong psychometric properties and sensitivity to developmental change in intellectual and developmental disabilities. However, whether gains in NIHTB-CB Crystallized Cognition reflect improvements in broader verbal abilities is unclear, and this has implications for clinical interpretation of the measure in the context of treatment studies. Two-hundred sixty-three participants completed NIHTB-CB Crystalized Cognition subtests (Picture Vocabulary, Oral Reading Recognition) and Stanford-Binet 5th ed. subtests (Verbal Knowledge, Verbal Fluid Reasoning) at baseline and at two-year follow-up. Bivariate latent change score models examined whether changes in Crystalized Cognition were related to changes in broader verbal skills. Changes in Crystalized Cognition were significantly related to changes in Verbal Knowledge (β = 7.92, p = .009) and Verbal Fluid Reasoning (β = 4.91, p = .018). Higher baseline Crystalized Cognition predicted greater improvement in these verbal domains, while higher initial verbal scores also predicted more Crystalized Cognition growth. Change in the NIHTB-CB Crystalized Composite was significantly related to growth in verbal reasoning in children and young adults with IDD. This may indicate that the Crystalized Composite is a useful proxy for broader verbal skills, underscoring its clinical relevance.