Neighborhood Density and Word Frequency Predict Vocabulary Size in Toddlers

Purpose: To document the lexical characteristics of neighborhood density (ND) and word frequency (WF) in the lexicons of a large sample of English-speaking toddlers. Method: Parents of 222 British-English-speaking children aged 27(+/-3) months completed a British adaptation of the MacArthur-Bates Communicative Development Inventory: Words and Sentences (MCDI; Klee & Harrison, 2001). Child words were coded for ND and WF, and the relationships among vocabulary, ND, and WF were examined. A cut-point of -1 SD below the mean on the MCDI classified children into one of two groups: low or high vocabulary size. Group differences on ND and WF were examined using nonparametric statistics. Results: In a hierarchical regression, ND and WF accounted for 47% and 14% of unique variance in MCDI scores, respectively. Low-vocabulary children scored significantly higher on ND and significantly lower on WF than did high-vocabulary children, but there was more variability in ND and WF for children at the lowest points of the vocabulary continuum. Conclusion: Children at the lowest points of a continuum of vocabulary size may be extracting statistical properties of the input language in a manner quite different from their more able age peers.