Development of the McMaster Cough Severity Questionnaire (MCSQ) for patients with chronic cough

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Background: Cough severity is an important endpoint to assess the impact of therapies for refractory or unexplained chronic cough (RCC/UCC). Objective: To develop a patient-reported outcome measure addressing cough severity in patients with RCC/UCC. Methods: Phase 1: A systematic survey, focus groups, and expert consultation generated 51 items. Phase 2: From a list of 51 items, 100 patients identified those they had experienced in the previous year and rated their importance on a 5-point scale. The draft MCSQ included items reported to occur most frequently and that had the highest importance scores. Patient feedback on the draft MCSQ led to elimination of redundant items. Phase 3: Another 100 patients completed the draft MCSQ, from which we performed an exploratory factor analysis to further refine items on the MCSQ and assess its construct validity and internal consistency. Results: Item reduction using the impact method led to selection of 15 items for the draft MCSQ. Patient feedback on the 15 items led to elimination of 5 redundant items. An exploratory factor analysis of the 10-item MCSQ led to selection of two domains (intensity and frequency), elimination of one item that demonstrated substantial cross-loading, and another that had high inter-item correlations. The final MCSQ consisted of 8 items, each with a one-week recall period, under two domains. The 8-item MCSQ had high internal consistency (α=0.89) and high cross-sectional convergent validity (r=0.76 [95% CI 0.66 to 0.83]) with the 100-mm cough severity visual analogue scale. Conclusions: Initial evidence supports the validity of the MCSQ. Further studies should assess its properties in measuring change over time.