Factors associated with the early language development of New Zealand children

Abstract

Problem under investigation. This project was undertaken to establish reliable, population-based normative data on the early language development of children growing up in New Zealand (NZ). The project had two aims: (1) to develop nationally representative norms for early vocabulary and grammar based on a NZ adaptation of the MacArthur-Bates Communicative Development Inventory: Words & Sentences (NZ CDI:WS) and (2) to examine their association with demographic, family and child variables. Methods. The target population was parents of monolingual, English-speaking children aged 16-30 months living in NZ. We aimed to collect data on 100 girls and 100 boys at each month of age via a dedicated website (www.kidswords.org), where parents completed an online version of the NZ CDI:WS and a demographic questionnaire. Parents of over 2,600 children participated, representing 87% of our target. 51% of the children were girls; 62% were first-born; 3% were twins and all 16 regions of NZ were represented. Results and conclusion. Children’s expressive vocabulary size ranged from a mean of 67 words (95% CI = 58, 76) at age 16 months to 477 words (95% CI = 453, 502) at 30 months. Age accounted for 47% of the variance in vocabulary size in this age range, while sex, birth order, and whether the child was a twin accounted for 3% additional variance. Similarly, age accounted for 42% of the variance in grammatical complexity scores (CDI section E), with the same factors accounting for 1.6% additional variance. Vocabulary size and grammatical complexity scores were highly correlated (r = .85; 95% CI = .84, 1.00). Percentiles for vocabulary size will be presented and cross-linguistic comparisons will be made between the NZ data and CDI data from other countries. Further uses of the data collected from this project will be discussed.