Development of a Vocabulary Inventory for English-Mandarin Dual-Language-Learning Infants and Toddlers

The science of early bilingual language development requires accurate documentation of the words that infants/toddlers acquire in each language to address questions about language transfer, mutual exclusivity, conceptual vocabulary growth, etc. We developed the Dual Language Learners English–Mandarin (DLL-EM) inventories to measure the vocabularies of English–Mandarin infants/toddlers. The inventories expand on American English and Beijing Mandarin MacArthur–Bates Communicative Development Inventories (CDIs) with full translation equivalents and Mandarin dialect options, while retaining original words on CDI forms. We quantified the psychometric properties of the DLL-EM (Study 1) using Item Response Theory based on American English and Beijing Mandarin CDI data from Wordbank and Web-CDI (n = 1880, Level 1; n = 7536, Level 2). The DLL-EM demonstrated near-perfect correlations with estimated English and Mandarin CDI scores. We interviewed a small group of mothers to characterize the composition of their toddlers’ vocabularies in English and Mandarin (Study 2, N = 30). The DLL-EM required ~15 min to administer, yielded large differences among toddlers in English and Mandarin vocabularies, and provided insights into toddlers’ total and conceptual vocabularies that diverged from estimates yielded by nonmatching original CDI forms. The DLL-EM provides a valid, culturally responsive tool for assessing vocabularies of English–Mandarin dual language learners, which is essential for researchers, educators, and clinicians.