Reconceptualizing developmental language disorder as a spectrum disorder: issues and evidence.
Hope S Lancaster, Stephen Camarata
PMID 30426606WHAT IT FOUND
In a kindergarten DLD sample, children did not form clear diagnostic subtypes; language and performance IQ scores varied along a shared continuum.
The results support a spectrum model rather than subtype labels.
Key findings
01The minimum BIC corresponded to 18 clusters, which was too many to map onto clinical subtypes.
02The clustering was not explained by chance, which supports a continuum/spectrum structure.
03The large number of clusters supported an individual differences model, but the non-random clustering did not support that model.
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The analysis used one kindergarten database and only the language and performance IQ measures available in that database. It did not include norm-referenced pragmatic language tasks, so it could not test pragmatic language disorder subtypes well. The main cluster analysis included only children already classified as DLD, not typical language peers, which limits tests of individual differences. Different clustering methods did not yield identical clusters, so the conclusion should not rest on one clustering method alone. The study did not test whether a spectrum approach improves assessment or treatment outcomes. The sample was United States kindergarten children, so it says little about older children or other languages and cultures.
Declared interests
The authors report no conflicts of interest.
The easy way to misread this
Do not conclude that DLD has no subtypes in all ages or settings. This was a cluster analysis of one kindergarten database with limited measures, and it did not test treatment outcomes. It also did not show that a spectrum model is proven; it only supports testing DLD as a spectrum in future samples.