Development and validation of a new questionnaire appropriate to assess respiratory symptoms in current and former smokers without chronic obstructive pulmonary disease: The Respiratory Symptom Questionnaire (RSQ)

Background: Smokers who switch completely to electronic nicotine delivery systems (ENDS) may experience reductions in respiratory symptoms (e.g., cough, wheezing). Assessing such symptoms among smokers without respiratory disease using existing respiratory symptom questionnaires is challenging, as these questionnaires are intended for patient populations, such as those with chronic obstructive pulmonary disease (COPD). The current study aimed to develop a respiratory symptom questionnaire appropriate for current and former smokers including those without COPD. Methods: : This research included 3 phases. First, a draft respiratory symptom questionnaire (RSQ) was generated with input from subject matter experts. Second, the RSQ was refined through waves of cognitive debriefing interviews ( n =49) with adult current smokers (Smokers) and former smokers who switched completely to ENDS for 6+ months (Switchers). Finally, Smokers ( n = 202), Switchers ( n =208), and Former Smokers (no tobacco use in 6+ months; smoked 10+ years; n =200) completed the RSQ for purposes of the quantitative psychometric evaluation. Results: : The first two phases produced a 5-item RSQ that captured relevant symptoms and was interpreted as intended. During Phase 3 the RSQ was evaluated within the context of the graded response model (GRM). GRM assumptions of ordinality of response categories and unidimensionality were met. Test-retest reliability over a 1-week interval was good, and results provided support for convergent validity. Significant differences between Smokers’ and Former Smokers’ RSQ scores provide initial support for the RSQ’s ability to detect change in respiratory symptoms over time. In exploratory analyses, Switchers’ RSQ scores were significantly lower than Smokers’ scores, but not significantly different from Former Smokers’. Conclusion: Findings from this rigorous instrument development and validation study provide strong support for the reliability and validity of the RSQ as a measure of respiratory symptoms in adult current and former smokers, including those who may be at risk for developing COPD. The finding that RSQ scores among former smokers who had switched completely to ENDS were significantly lower than current smokers’ scores and similar to the scores of former smokers who had quit suggests that switching from cigarettes to ENDS may improve respiratory health.