Child vocabulary across the second year: Stability and continuity for reporter comparisons and a cumulative score

Mothers, fathers and caregivers in 29 families completed the Infant and Toddler Forms of Dutch adaptations of the MacArthur Communicative Development Inventories (CDI) for the same children at 1;1 and 1;8, respectively. We computed CDI Cumulative Scores, which credit the child with the best score for each item on the CDI as checked by any single reporter. We then computed comprehension and production scores for each reporter and for the cumulative score. Different reporters assess a particular child's communicative abilities differently. Mothers', fathers' and caregivers' comprehension scores intercorrelated, as did their production scores. Reporters' comprehension and production scores were lower than their respective cumulative comprehension and production scores. For all reporters and the cumulative score, we found significant stability in comprehension and production from 1;1 to 1;8 and significant increases in average comprehension and production.