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Data from parent reports on 1,803 children--derived from a normative study of the MacArthur Communicative Development Inventories (CDIs)--are used to describe the typical course and the extent of variability in major features of communicative development between 8 and 30 months of age. The two instruments, one designed for 8-16-month-old infants, the other for 16-30-month-old toddlers, are both reliable and valid, confirming the value of parent reports that are based on contemporary behavior and a recognition format. Growth trends are described for children scoring at the 10th-, 25th-, 50th-, 75th-, and 90th-percentile levels on receptive and expressive vocabulary, actions and gestures, and a number of aspects of morphology and syntax. Extensive variability exists in the rate of lexical, gestural, and grammatical development. The wide variability across children in the time of onset and course of acquisition of these skills challenges the meaningfulness of the concept of the modal child. At the same time, moderate to high intercorrelations are found among the different skills both concurrently and predictively (across a 6-month period). Sex differences consistently favor females; however, these are very small, typically accounting for 1%-2% of the variance. The effects of SES and birth order are even smaller within this age range. The inventories offer objective criteria for defining typicality and exceptionality, and their cost effectiveness facilitates the aggregation of large data sets needed to address many issues of contemporary theoretical interest. The present data also offer unusually detailed information on the course of development of individual lexical, gestural, and grammatical items and features. Adaptations of the CDIs to other languages have opened new possibilities for cross-linguistic explorations of sequence, rate, and variability of communicative development.

The MacArthur Communicative Development Inventories (CDIs) are a pair of widely used parent-report instruments for assessing communicative skills in infants and toddlers. This report describes short-form versions of the CDIs and their development, summarizes newly available normative data and psychometric properties of the instruments, and discusses research and clinical applications. The infant short form (Level I, for 8- to 18-month-olds) contains an 89-word checklist for vocabulary comprehension and production. The two parallel versions of the toddler short form (Level II, Forms A and B, for 16- to 30-month-olds) each contain a 100-word vocabulary production checklist and a question about word combinations. The forms may also be useful with developmentally delayed children beyond the specified age ranges. Copies of the short forms and the normative tables appear in the appendices.

Results are reported for stylistic and developmental aspects of vocabulary composition for 1,803 children and families who participated in the tri-city norming of a new parental report instrument, the Mac Arthur Communicative Development Inventories. We replicate previous studies with small samples showing extensive variation in use of common nouns between age o;8 and 1 ;4 (i.e. 'referential style'), and in the proportion of vocabulary made up of closed-class words between 154 and 2;6 (i.e. 'analytic' vs. 'holistic' style). However, both style dimensions are confounded with developmental changes in the composition of the [*]

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Studies examining factors that influence when words are learned typically investigate one lexical category or a small set of words. We provide the first evaluation of the relation between input frequency and age of acquisition for a large sample of words. The MacArthur-Bates Communicative Development Inventory provides norming data on age of acquisition for 562 individual words collected from the parents of children aged 0 ; 8 to 2 ; 6. The CHILDES database provides estimates of frequency with which parents use these words with their children (age: 0 ; 7-7 ; 5; mean age: 36 months). For production, across all words higher parental frequency is associated with later acquisition. Within lexical categories, however, higher frequency is related to earlier acquisition. For comprehension, parental frequency correlates significantly with the age of acquisition only for common nouns. Frequency effects change with development. Thus, frequency impacts vocabulary acquisition in a complex interaction with category, modality and developmental stage.

When carefully assessed and analysed, parent report can provide a valuable overall evaluation of children's language at 20 months. Norming information and validity coefficients are presented here for a vocabulary checklist assessment included in the Early Language Inventory. Normative data are provided for fullterm, preterm, and precocious samples, including selected vocabulatory subsets that are indicative of early language learning style. The vocabulary checklist has substantial validity as indexed by correlations with the Bayley Scales of Infant Development and particularly with a language subscale derived from that test.

The MacArthur-Bates Communicative Development Inventories (CDI; Dale, 1996; Fenson et al., 1994), parent reports about language skills, are being used increasingly in studies of theoretical and public health importance. This study (N = 113) correlated scores on the CDI at ages 2 and 3 years with scores at age 3 years on tests of cognition and receptive language and measures from parent-child conversation. Associations indicated reasonable concurrent and predictive validity. The findings suggest that satisfactory vocabulary scores at age 2 are likely to predict normal language skills at age 3, although some children with limited skills at age 3 will have had satisfactory scores at age 2. Many children with poor vocabulary scores at 2 will have normal skills at 3.