Master Kari-Anne B. Næss' avhandling for graden ph.d.

Language and Reading Development in Children with Down Syndrome,

This article-based thesis addresses the language profile in children with Down syndrome by comparing their results to typically developing children at the same nonverbal mental age using two different approaches: meta-analysis of earlier cross-sectional studies and a longitudinal empirical study. The dual approach was designed in order to achieve as valid a result as possible. The first meta-analysis was planned to review the state of the art in the field of language and verbal short-term memory skills in children with Down syndrome and to assess what needs to be done in further studies. Based on the results and methodological challenges experienced in the first meta-analysis, the longitudinal empirical study was carefully planned. The results from the two different approaches support each other in showing that children with Down syndrome have deficits on a wide range of language measures. The longitudinal study gave additional information about progress over time and uncovered important predictors of development. Children with Down syndrome showed slower development compared to typically developing children at the same nonverbal mental age. Differences in vocabulary and articulation were important predictors of variation in later vocabulary and grammatical development in children with Down syndrome. In order to start planning for an effective vocabulary intervention, the relationship between vocabulary and reading was explored using a meta-analysis on reading skills comparing children with Down syndrome and typically developing children matched on word recognition level. The result showed that children with Down syndrome had significantly weaker nonword decoding skills compared to the controls. Differences in vocabulary explained a high proportion of the variance in nonword decoding skills but were not a significant predictor. However, only four studies had included a measure of vocabulary and because of the very small sample the question about the relationship between vocabulary and reading skills should be investigated in further studies. In addition to the three articles summarised above, the extended abstract gives within a theoretical framework an overview of different methodological challenges and ethical dilemmas considered throughout the work with the studies included in this PhD.