Background: Patients with respiratory disease experience disturbed sleep, but there is no widely accepted measure of sleep impairment due to respiratory disease. We developed and evaluated the psychometric performance of a patient-reported measure to assess the impact on sleep due to respiratory disease, the COPD and Asthma Sleep Impact Scale (CASIS).
Methods: Identification of the items forming the CASIS was guided by patient interviews and focus groups. An observational study involving patients from the US and UK was then conducted to assess the psychometric characteristics of the measure.
Results: Qualitative data from 162 patients were used to develop the CASIS (n = 78 COPD; n = 84 asthma). The observational study included 311 patients with COPD and 324 patients with asthma. The final seven items used in the CASIS were identified based on factor and item response theory analyses. Internal consistency was 0.90 (COPD) and 0.92 (asthma), and test-retest reliability was 0.84 (both groups). In the COPD sample, CASIS scores were significantly correlated with the Saint George's Respiratory Questionnaire scores (all p < 0.0001) and differed significantly by patient-reported disease severity, exacerbation status, and overall health status (all p <or= 0.005). In the asthma sample, CASIS scores were significantly correlated with the Asthma Quality of Life Questionnaire scores (all p < 0.0001) and differed significantly by clinician and patient-reported disease severity, exacerbation status, and overall health status (all p <or= 0.0005).
Conclusion: The CASIS shows good internal consistency, test-retest reliability, and construct validity and may be useful in helping to understand the impact that COPD and asthma have on sleep outcomes.