Effectiveness of vocabulary interventions for individuals with Down syndrome, what can we learn, what’s missing, and where next?

During the process of scanning abstracts from our literature search on vocabulary interventions for children with Down syndrome, we are finding patterns with regards to the types of inclusion criteria not tending to be met; preventing us from including various articles in our review on this topic. While at the outset, we had expected to find a relatively small number of hits meeting all our inclusion criteria, we are finding even fewer than expected. The reason for the lack of articles being included is due to various reasons, but in particular to the lack of control groups in many of the studies in this area, and also due to the lack of studies specifically targeting vocabulary in children with Down syndrome. It is also worth noting that the only RCT that we are currently aware of involving vocabulary intervention for children with Down syndrome was itself primarily aiming to improve reading in children with Down syndrome. There is very little research assessing the effectiveness of vocabulary interventions for children with Down syndrome, and research in vocabulary-related areas is often lacking sufficient empirical quality to assess statistically whether the interventions are effective.

If we were to discard various inclusion criteria such that we could have more articles meet our criteria and enough to carry out a meta-analysis, this would reduce the quality and relevance of what goes into the meta-analysis and that in turn would simply be reflected in the quality and clarity of the meta-analysis results, and the conclusions and implications of those overall results. Such results would be of little value to those attempting to assess what is effective for improving vocabulary, and future directions. What we can do at this stage however, is carry out a systematic literature review on the various articles out there to get a grasp on the current state of the intervention literature and what may have theoretical relevance for future intervention approaches, as well as to consider the effectiveness of those very few studies in the area that do meet all or most of the inclusion criteria.  

Of course, interventions tend to be a fairly large investment of time and resources, with pre-tests, post-tests and various treatments. It is also worth keeping in mind the importance of well-researched theory behind the domain being trained, prior to the training itself being carried out. With regards to vocabulary, it is clearly an area that needs to be targeted in Down syndrome. Language generally, is often an area of weakness in individuals with Down syndrome, tending to be reported as delayed and below individuals’ other cognitive abilities.  While vocabulary has often been suggested to be a strength in children with Down syndrome compared to other areas of language that children tend to find particularly difficult e.g., grammar, it is important to note that vocabulary seems to be a bottleneck to develop other language skills, reading skills and social skills. Therefore improving vocabulary is a valuable goal. We also know that children with Down syndrome are likely to have poorer abilities to express vocabulary, relative to stronger vocabulary comprehension. Vocabulary interventions for those with Down syndrome need to use approaches specific to the needs of these children and consider their various strengths and weakness. It is important that children with Down syndrome feel engaged and motivated to participate in interventions that are aimed at them. We can also look to the findings of interventions that appear to work for typically developing children, or other populations, and explore areas related to vocabulary, and consider how these may be relevant or adapted for those with Down syndrome in order to develop an intervention that may succeed in improving vocabulary for them. One possibility that we have yet to explore is that there have been vocabulary interventions carried out that have not been published, e.g. because of null-results. We will attempt to find out about any unpublished cases to provide a full picture of types of vocabulary intervention research being carried out in the Down syndrome population.

With vocabulary such an important component of a child’s development it is an area that is deserving of attention, and we therefore feel positive about developing an RCT intervention in this area. It is apparent that more research is needed, and it is also worth us acknowledging of course that other domains as well as vocabulary are of course likely to be in need of empirical intervention research for those with Down syndrome. This research is needed for us to progress in the quality and success with which we educate children with Down syndrome in various areas.

Liz Smith & Kari-Anne Næss