Low verbal assessment with the Bayley-III

Recently, the authors have developed the Bayley-III-NL Low Verbal for developmental assessment of children with language impairment. The Low Verbal version consists of an accommodated cognition scale, and non-accommodated communication and motor scales. The purpose of the study was to evaluate the validity and added value of the Bayley-III-NL Low Verbal for children with a language impairment, in relation to the standard Bayley-III-NL for children without impairment. We administered the Bayley-III Low Verbal to 69 children with language impairment, and the standard Bayley-III-NL to 1132 children without impairments. We used an evaluation form for test administrators and interviews with developmental psychologists to evaluate the suitability of the Low Verbal version for the target group. We analyzed the test results using nonparametric item response theory (IRT) to investigate whether test results can be reasonably compared across the two groups. The results of the IRT analyses support the validity of the Bayley-III-NL Low Verbal: the test items do not suffer from differential item functioning (DIF) across the two groups, and thus measure the ability levels of interest in the same way. The results of the evaluation form and interviews confirm that the Bayley-III-NL Low Verbal has added value for testing children with a language impairment, especially for children up to 36 months old. It is also suitable for children with general developmental delay. We conclude that the Bayley-III-NL Low Verbal can validly assess the cognitive, language, and motor development of young children with a language impairment and is the preferred instrument for this target group.