Improving Measurement Efficiency of the Cough Severity Index With Item Response Theory

OBJECTIVE: The larynx is central to voice, breathing, swallowing, and cough-such that routinely tracking related outcomes can introduce burden. Within these assessments, the Cough Severity Index (CSI) is frequently deployed. We thus utilized item response theory (IRT) to determine: (1) which items confer the most information, (2) if proposed 5-item scales yield substantially differing discrimination and location parameters, compared to the 10-item instrument, and (3) whether a subset of items has more favorable characteristics as an initial assessment (i.e., for whether all 10 items are needed). METHODS: Item discrimination, location, and information parameters were calculated from 4240 consecutive CSI responses. Based on these data, 5-item subsets were proposed, evaluated, and compared with each other and the 10-item instrument via information function curves and receiver-operator characteristic (ROC) analyses. Performance of 5-item mean scores < 1 as a potential initial assessment for the full results was also assessed. RESULTS: Discrimination parameters ranged from 0.65-2.76, with the greatest discrimination in items about embarrassment or avoiding places due to cough. These data, along with residual item correlations and location parameters, delineated a 5-item subset, which also incorporated cough when lying down, affecting voice, and upset by cough for comparative analysis. ROC-AUCs revealed no difference between the 5-item subset and parent 10-item instrument in ability to discriminate cough-specific clinical diagnoses. One 5-item subset performed better as an initial assessment (mean 4.9, 95% CI 4.7-5.2). CONCLUSION: IRT data identified a 5-item CSI subset which reflects the cough trait and provides an initial efficient assessment mechanism.