The discrepancy hypothesis in children with language disorders: does it work?

Objectives: Analysis of the relationship between verbal and nonverbal development in children with language problems.

Methods: From 134 children enrolled in a multidisciplinary diagnostic procedure in a speech and hearing clinic and diagnosed as having a language disorder, the language comprehension score (LCQ) and the nonverbal IQ score (SON-IQ) were compared. t-Tests were used to test whether the children's mean LCQ differs from their mean SON-IQ and to test whether the children with an inadequate LCQ differ from children with an adequate LCQ with respect to discrepancy. Plots inspired by Bland and Altman [18] display the measurement of mean value of verbal and nonverbal development against the discrepancy between these scores.

Results: All children had a language production problem (inadequate GDS). Out of the 57 children with an adequate language comprehension (LCQ>80), 16 children (28%) show a discrepancy of 10 quotient points or more between their LCQ and SON-IQ. Out of the 77 children with an inadequate language comprehension (LCQ80 the discrepancy is not significant (p=0.084).

Conclusions: The discrepancy hypothesis, in our opinion, must be modified. There is not only verbal and nonverbal functioning but there is language production, language comprehension and nonverbal learning abilities. Between these three aspects discrepancies can be found. In 43% of the children there is a discrepancy between language production and language comprehension. When children also show language comprehension problems, 58% of these children show a discrepancy with nonverbal functioning.