Progress Toward Estimating the Minimal ClinicalImportant Difference of Intelligibility: A Crowdsourced Perceptual Experiment

Purpose: The purpose of the current study was to estimate the minimal cally important difference (MCID) of sentence intelligibility in control speakand in speakers with dysarthria due to multiple sclerosis (MS) and Parkinsdisease (PD). Method: Sixteen control speakers, 16 speakers with MS, and 16 speakers PD were audio-recorded reading aloud sentences in habitual, clear, fast, loand slow speaking conditions. Two hundred forty nonexpert crowdsourced teners heard paired conditions of the same sentence content from a speand indicated if one condition was more understandable than another. Listenthen used the Global Ratings of Change (GROC) Scale to indicate how mmore understandable that condition was than the other. Listener ratings wcompared with objective intelligibility scores obtained previously via orthgraphic transcriptions from nonexpert listeners. Receiver operating characteritic (ROC) curves and average magnitude of intelligibility difference per levethe GROC Scale were evaluated to determine the sensitivity, specificity, accuracy of potential cutoff scores in intelligibility for establishing thresholds important change. Results: MCIDs derived from the ROC curves were invalid. However, the aage magnitude of intelligibility difference derived valid and useful thresholThe MCID of intelligibility was determined to be about 7% for a small amoudifference and about 15% for a large amount of difference. Conclusions: This work demonstrates the feasibility of the novel experimenparadigm for collecting crowdsourced perceptual data to estimate MCIDResults provide empirical evidence that clinical tools for the perception of iligibility by nonexpert listeners could consist of three categories, which emerfrom the data (“no difference,” “a little bit of difference,” “a lot of differenThe current work is a critical step toward development of a universal langwith which to evaluate changes in intelligibility as a result of neurological indisease progression, and speech-language therapy.