Bantu on the brain: Community-informed adaptations of the Macarthur-Bates Communication Development Index to contemporary Zambian languages using item response theory

The MacArthur-Bates Communication Development Inventories (MB-CDI) are a widely used set of tools to assess language acquisition in early childhood. Although it has been adapted in 120 languages, there is not a linguistic nor culturally congruent tool for any of the 72 Zambian Bantu languages. This manuscript describes the process to adapt the MB-CDI for two of the most spoken languages in Zambia: Nyanja and Bemba. Using mixed-methods with caregivers of children aged 16 to 30 months in Lusaka, Zambia, we have constructed two Bantu-language adaptations of the MD-CDI: Words and Sentences short form. Two focus group discussions of caregivers were conducted, one in Nyanja (n=10) and one in Bemba (n=10). The goal of the focus groups was to generate a list of commonly heard words in early childhood. Facilitators then administered individual assessment surveys to Bemba (n=77) and Nyanja (n=109) caregivers to determine which words from the generated lists their child (aged 16-30 months) had acquired in productive speech. We then fitted a 2-parameter item response theory model to our data to reflect 100 words, characterized by a range of difficulty and highest ability to effectively distinguish between different levels of language proficiency. Our adapted MB-CDI for Bemba and Nyanja is a language acquisition assessment tool for ages 16-30 months to measure language development in the two most spoken Bantu languages in Zambia.