Effect Size for Single-Subject Design in Phonological Treatment

In 1984, Jacobson, Follette, and Revenstorf defined clinically significant change as the extent to which therapy moves someone outside the range of the dysfunctional population or within the range of the functional population. In the present article, ways of operationalizing this definition are described, and examples are used to show how clients can be categorized on the basis of this definition. A reliable change index (RC) is also proposed to determine whether the magnitude of change for a given client is statistically reliable. The inclusion of the RC leads to a twofold criterion for clinically significant change.

A brief, processing-dependent, nonword repetition task, designed to minimize biases associated with traditional language tests, was investigated. In Study 1, no overlap in nonword repetition performance was found between a group of 20 school-age children enrolled in language intervention (LI) and a group of 20 age-matched peers developing language normally (LN). In Study 2, a comparison of likelihood ratios for the nonword repetition task and for a traditional language test revealed that nonword repetition distinguished between children independently identified as LI and LN with a high degree of accuracy, by contrast with the traditional language test. Nonword repetition may have considerable clinical utility as a screening measure for language impairment in children. Information on the likelihood ratios associated with all diagnostic tests of language is badly needed.