Classification of adults for family studies of developmental language disorders

A variety of approaches has been used to classify the status of adult subjects in familial studies of developmental language disorders. In this report, we directly compare the results of four different methods that appear in the research literature. Two of the approaches rely on case history reports, and two are performance-based methods. Subjects included 24 parents (12 mothers, 12 fathers) of children with developmental language disorders and 24 unrelated adult control subjects (12 female, 12 male) who completed case history items and standardized language testing designed for classification purposes. All classification methods identified more parents than control subjects as "affected". However, classification by case history methods resulted in fewer affected adults than classification through standardized testing. This outcome suggests that the variability in classification rates in studies to date may be the result of method rather than subject sample differences.