Validation of the NIH Toolbox Cognitive Battery in intellectual disability

Abstract

Objective: To advance the science of cognitive outcome measurement for individuals with intellectual disability (ID), we established administration guidelines and evaluated the psychometric properties of the NIH-Toolbox Cognitive Battery (NIHTB-CB) for use in clinical research.

Methods: We assessed feasibility, test-retest reliability, and convergent validity of the NIHTB-CB (measuring executive function, processing speed, memory, and language) by assessing 242 individuals with fragile X syndrome (FXS), Down syndrome (DS), and other ID, ages 6 through 25 years, with retesting completed after 1 month. To facilitate accessibility and measurement accuracy, we developed accommodations and standard assessment guidelines, documented in an e-manual. Finally, we assessed the sensitivity of the battery to expected syndrome-specific cognitive phenotypes.

Results: Above a mental age of 5.0 years, all tests had excellent feasibility. More varied feasibility across tests was seen between mental ages of 3 and 4 years. Reliability and convergent validity ranged from moderate to strong. Each test and the Crystallized and Fluid Composite scores correlated moderately to strongly with IQ, and the Crystallized Composite had modest correlations with adaptive behavior. The NIHTB-CB showed known-groups validity by detecting expected executive function deficits in FXS and a receptive language deficit in DS.

Conclusion: The NIHTB-CB is a reliable and valid test battery for children and young adults with ID with a mental age of ≈5 years and above. Adaptations for very low-functioning or younger children with ID are needed for some subtests to expand the developmental range of the battery. Studies examining sensitivity to developmental and treatment changes are now warranted.

Figure 1. NIHTB-CB cognitive function composite score distribution and association with FSIQ

(A) Histogram showing the true distribution of cognitive function composite scores in the full sample of individuals with intellectual disability (ID). The NIH Toolbox Cognitive Battery (NIHTB-CB) current floor (winsorized at 54; vertical blue line) excluded more than half of the present sample from more accurate measurement below that level. (B) Association between the deviation-based cognitive function composite and deviation-based full-scale IQ (FSIQ) by group.

Figure 2. Profile plot of NIH Toolbox Cognitive Battery test z scores by group

The z scores on each test (representing group performance relative to the general population average performance) are shown, derived from the mixed-model analysis of variance, adjusted for IQ. A z score of 0 (horizontal line at top) represents the average performance in the general population normative sample. The z scores <0 represent the number of SDs below the general population average for the chronologic age band. Error bars represent 95% confidence intervals. *Comparison between fragile X syndrome (FXS) and intellectual disability (ID) of other or unknown cause. †Comparison between FXS and Down syndrome. *p < 0.05; **p < 0.01; ***p < 0.001; †p < 0.05; ††p < 0.01; †††p < 0.001. DCCS = Dimensional Change Card Sort; LS = List Sorting Working Memory; OR = Oral Reading and Recognition; PC = Pattern Comparison Processing Speed; PSM = Picture Sequence Memory; PVT = Picture Vocabulary.