Comparing productive vocabulary measures from the CDI and a systematic diary study

Area of Science:

• Child language acquisition
• Developmental psychology
• Lexical development

Background:

• Systematic diary studies offer detailed insights into early language development.
• The MacArthur Communicative Development Inventories (CDI) spoken vocabulary checklist is a common tool for assessing early vocabulary.
• Comparing different data collection methods is crucial for understanding their respective strengths and limitations.

Observation:

• Expressive vocabulary data from a male child's diary study were compared with hypothetical CDI data.
• Comparisons focused on vocabulary size over time, lexical class proportions, and growth curve modeling.
• The study period spanned from 9 months to 2 years of age.

Findings:

• The CDI consistently underestimated vocabulary size compared to the diary study, with underestimation increasing with vocabulary growth.
• The proportion of words from the diary study that appeared on the CDI varied significantly by lexical class (noun, predicate, closed class, other).
• Logistic growth curves provided the best fit for modeling vocabulary development, regardless of whether diary or CDI data were used.

Implications:

• Longitudinal use of the CDI may require adjustments to account for systematic underestimation.
• Understanding lexical class-specific differences is important for accurate vocabulary assessment.
• The findings inform the interpretation of vocabulary data collected via the CDI in research and clinical settings.