Double it up: Vocabulary size comparisons between UK bilingual and monolingual toddlers.
Level 3 - non-randomized controlled study
Cross-sectional non-randomized comparative study with concurrent control group.
PubMed 37792587 · doi:10.1111/infa.12562
What was done
Parent-report vocabulary questionnaires were used to compare vocabulary comprehension and production between bilingual toddlers (aged 12–36 months) in the United Kingdom and age-matched UK English monolingual toddlers.
What was found
The abstract reports directional comparisons without exact quantitative figures: - English-only vocabulary size was smaller in bilingual toddlers than in monolinguals for both comprehension and production. - Conceptual vocabulary scoring eliminated the comprehension gap between groups. - Conceptual scoring reduced the production gap, though the difference remained statistically significant in favor of monolinguals. - Total vocabulary (combining words across both languages) was greater in bilinguals than monolinguals in both comprehension and production, attributed to a high proportion of translation doublets.
Why it matters
Assessing bilingual toddlers solely in one language underestimates their linguistic repertoire; conceptual and cross-linguistic total vocabulary metrics offer a more accurate measure of lexical development.
Limits
The abstract does not state the sample size, specific bilingual language pairings, or numerical effect sizes and confidence intervals. Lexical size was measured exclusively via parent-report questionnaires rather than direct behavioral assessment.