Diary vs. representative checklist assessment of productive vocabulary

Twenty-four infants were followed longitudinally from 1.2 to 1.10. Parents maintained diaries of the child's spoken words and at two-month intervals completed a representative checklist of words produced. There was good agreement across the two instruments and robust month-to-month correlations for both. However, the overall pattern of results suggests that the diary method is more effective during the early emergence of language and the representative checklist method is more effective late in the second year when vocabulary size becomes relatively large. Accurate longitudinal assessment of vocabulary may require a combination of the diary and checklist approaches.