Psychometric performance and responsiveness of the functional outcomes of sleep questionnaire and sleep apnea quality of life index in a randomized trial: The HomePAP study

Study Objectives: Measures of health-related quality of life (HRQL) specific for sleep disorders have had limited psychometric evaluation in the context of randomized controlled trials (RCTs). We investigated the psychometric properties of the Functional Outcomes of Sleep Questionnaire (FOSQ) and Sleep Apnea Quality of Life Index (SAQLI). We evaluated the FOSQ and SAQLI construct and criterion validity, determined a minimally important difference, and assessed for associations of responsiveness to baseline subject characteristics and continuous positive airway pressure (CPAP) adherence in a RCT population. Design: Secondary analysis of data collected in a multisite RCT of home versus laboratory-based diagnosis and treatment of obstructive sleep apnea (HomePAP trial). Participants: Individuals enrolled in the HomePAP trial (n = 335). Interventions: N/A. Measurement and Results: The FOSQ and SAQLI subscores demonstrated high reliability and criterion validity, correlating with Medical Outcomes Study 36-Item Short Form Survey domains. Correlations were weaker with the Epworth Sleepiness Scale (ESS). Both the FOSQ and SAQLI scores improved after 3 mo with CPAP therapy. Averaging 4 h or more of CPAP use was associated with an increase in the FOSQ beyond the minimally important difference. Baseline depressive symptoms and sleepiness predicted FOSQ and SAQLI responsiveness; demographic, objective obstructive sleep apnea (OSA) severity and sleep habits were not predictive in linear regression. Conclusions: The Functional Outcomes of Sleep Questionnaire (FOSQ) and Sleep Apnea Quality of Life Index (SAQLI) are responsive to CPAP intervention, with the FOSQ being more sensitive to differences in CPAP adherence than the SAQLI. These instruments provide unique information about health outcomes beyond that provided by changes in physiological measures of OSA severity (apnea-hypopnea index).