Abstract
BackgroundThe Respiratory Symptoms Questionnaire (RSQ) is a novel, four-item patient-reported diagnosis-agnostic tool designed to assess the frequency of respiratory symptoms and their impact on activity, without specifying a particular diagnosis. Our objective was to examine its validity in patients with asthma and/or chronic obstructive pulmonary disease (COPD).MethodsBaseline data were randomly sampled from patients who completed the RSQ in the NOVELTY study (ClinicalTrials.gov: NCT02760329). The total sample (n=1530) comprised three randomly selected samples (n=510 each) from each physician-assigned diagnostic group (asthma, asthma+COPD and COPD). The internal consistency and structural validity of the RSQ were evaluated using exploratory and confirmatory factor analyses; psychometric performance was observed using Classical Test Theory and Item Response Theory analyses.ResultsFor the total sample, the mean±sd RSQ score was 5.6±4.3 (range 0–16). Irrespective of diagnosis, the internal consistency of items was uniformly adequate (Cronbach's α=0.76–0.80). All items had high factor loadings and structural characteristics of the measure were invariant across groups. Using the total sample, RSQ items informatively covered the θ score range of –2.0 to 2.8, with discrimination coefficients for individual items being high to very high (1.7–2.6). Strong convergent correlations were observed between the RSQ and the St George's Respiratory Questionnaire (0.77, p<0.001).ConclusionsThe RSQ is a valid, brief, patient-reported tool for assessing respiratory symptoms in patients across the whole spectrum of asthma and/or COPD, rather than using different questionnaires for each diagnosis. It can be used for monitoring respiratory symptoms in clinical practice, clinical trials and real-world studies.
Highlights
Respiratory symptoms are common and troublesome across the spectrum of obstructive lung disease, and are integral to the definitions of asthma and chronic obstructive pulmonary disease (COPD) [1, 2]
Some questions about general respiratory symptoms are included in several health-related quality-of-life questionnaires validated for use in asthma or COPD, but only two health status questionnaires have been validated for use in both conditions: the Airways Questionnaire 20 (AQ20) [14, 15] and St George’s Respiratory Questionnaire (SGRQ) [11, 16]
Primary objectives The primary objectives were to: 1) assess the internal consistency, unidimensionality and structural validity of the Respiratory Symptoms Questionnaire (RSQ) to evaluate the coherence of the RSQ measure, and assess the structural and measurement invariance of the RSQ across diagnostic groups using confirmatory factor analysis; 2) examine the linearity of RSQ item response associated with physician-assessed severity categories using Classical Test Theory; 3) examine RSQ item information functions, to evaluate whether similar profiles were found across diagnostic groups and evaluate RSQ item response characteristics over the observed range of criterion metrics; and 4) examine the differential performance of RSQ items to sex and physician-assigned diagnosis using Item Response Theory, to determine the equivalence of RSQ item function for groups of interest
Summary
Respiratory symptoms are common and troublesome across the spectrum of obstructive lung disease, and are integral to the definitions of asthma and chronic obstructive pulmonary disease (COPD) [1, 2]. Many questionnaires that assess the frequency, impact or control of respiratory symptoms are designed for patients with a confirmed diagnosis of either asthma or COPD [1, 2]. Conclusions: The RSQ is a valid, brief, patient-reported tool for assessing respiratory symptoms in patients across the whole spectrum of asthma and/or COPD, rather than using different questionnaires for each diagnosis. It can be used for monitoring respiratory symptoms in clinical practice, clinical trials and real-world studies
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