Measuring Speech Comprehensibility in Students with Down Syndrome

Purpose There is an ongoing need to develop assessments of spontaneous speech that focus on whether the child's utterances are comprehensible to listeners. This study sought to identify the attributes of a stable ratings-based measure of speech comprehensibility, which enabled examining the criterion-related validity of an orthography-based measure of the comprehensibility of conversational speech in students with Down syndrome. Method Participants were 10 elementary school students with Down syndrome and 4 unfamiliar adult raters. Averaged across-observer Likert ratings of speech comprehensibility were called a ratings-based measure of speech comprehensibility. The proportion of utterance attempts fully glossed constituted an orthography-based measure of speech comprehensibility. Results Averaging across 4 raters on four 5-min segments produced a reliable (G = .83) ratings-based measure of speech comprehensibility. The ratings-based measure was strongly ( r > .80) correlated with the orthography-based measure for both the same and different conversational samples. Conclusion Reliable and valid measures of speech comprehensibility are achievable with the resources available to many researchers and some clinicians.