EXAMINATION OF THE STABILITY OF 2 METHODS OF DEFINING SPECIFIC LANGUAGE IMPAIRMENT

Two commonly applied methods of differentially classifying language-de layed children as either specifically language impaired or development al lag language impaired (i.e., children with low IQ and low language performance) were examined for stability over I-and 2-year periods. On e classification method, following the DSM III-R guidelines, was based on an absolute cut-off level for performance on a measure of cognitiv e ability, in conjunction with other exclusionary criteria (i.e., lang uage delay that is not the result of hearing loss, social-emotional di sorder, etc.). The second classification method included the same abso lute cut-off for cognitive ability as the DSM III-R guidelines, but it also required that a minimum relative difference be present between t he general cognitive performance and the language performance. These t wo methods were examined for differences in classification of children , as well as for stability of classification across time. We used the McCarthy Scales of Children's Abilities Perceptual-Performance Index a s the cognitive measure and the Peabody Picture Vocabulary Test-Revise d and the Test of Early Language Development as language performance m easures. Results indicated significant differences in classification b etween the two methods of defining SLI, as well as substantial changes in classification over time using either method. Alternative classifi cation systems are discussed.