Sometimes larger, sometimes smaller: Measuring vocabulary in monolingual and bilingual infants and toddlers.
Level 3 - non-randomized controlled study
Cross-sectional comparative cohort study evaluating vocabulary metrics across monolingual and bilingual children.
PubMed 38283538 · doi:10.1177/01427237231204167
What was done
Parents of 743 infants and toddlers aged 8–33 months learning French, English, or both completed the MacArthur-Bates Communicative Development Inventories (CDI). The study compared monolingual vocabulary sizes against multiple bilingual metrics: total combined word count across both languages, conceptual vocabulary size (number of distinct lexicalized concepts), and single-language vocabulary size.
What was found
The abstract reports no exact numerical values or effect sizes. Compared with monolingual children, bilinguals had larger expressive and receptive total word vocabularies, similarly sized receptive concept vocabularies, smaller expressive concept vocabularies, and smaller single-language vocabularies.
Why it matters
This study shows that diagnostic and developmental evaluations of bilingual children can produce contradictory results—showing an advantage, equivalence, or deficit—depending entirely on the specific vocabulary metric used.
Limits
The abstract provides no quantitative data, error margins, or statistical significance levels. Data relied exclusively on parent-reported checklists rather than direct clinician observation, and the sample was limited to English- and/or French-learning children.