The McMaster Cough Severity Questionnaire (MCSQ): a cough severity instrument for patients with refractory chronic cough

BACKGROUND: Cough severity represents an important end-point to assess the impact of therapies for patients with refractory chronic cough (RCC). Our objective was to develop a new patient-reported outcome measure addressing cough severity in patients with RCC. METHODS: Phase 1 (item generation): a systematic survey, focus groups and expert consultation generated 51 items. Phase 2 (item reduction): 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 McMaster Cough Severity Questionnaire (MCSQ) included items reported to occur most frequently and that had the highest importance scores. Patient feedback on the MCSQ led to elimination of redundant items. Another 100 patients completed the MCSQ, from which we performed an exploratory factor analysis and a Rasch analysis to further refine items on the MCSQ. RESULTS: Previous publications report on the details of Phase 1. Phase 2 led to selection of 15 items from the initial 51. Patient feedback on the 15 items led to elimination of five redundant items. An exploratory factor analysis of the 10-item MCSQ led to the selection of two domains, and the elimination of one item that demonstrated cross-loading and another that had high inter-item correlations. A Rasch analysis of the 8-item MCSQ confirmed that the response options functioned in a logically progressive manner and that no items exhibited differential item functioning. The final 8-item MCSQ has a 1-week recall period and includes two domains (intensity and frequency). The 8-item MCSQ had high internal consistency (Cronbach's α=0.89), proved able to distinguish different levels of cough severity (person separation index 0.89) and demonstrated high cross-sectional convergent validity (Pearson's correlation 0.76, 95% CI 0.66-0.83) with the 100-mm cough severity visual analogue scale. CONCLUSIONS: Initial evidence supports the validity of the MCSQ, an 8-item instrument measuring cough severity in patients with RCC. Future studies should evaluate its properties in measuring change over time.