Introduction: The Functional Outcomes of Sleep Questionnaire (FOSQ), has been used in research and clinical practice to measure the impact of daytime sleepiness on activities of daily living. The purpose of this study was to develop a shorter version of the instrument (FOSQ-10) that may be more easily implemented in clinical practice.
Methods: Data from a study of CPAP-treated obstructive sleep apnea (OSA) patients (Sample 1) (n = 155, AHI = 63 +/- 31) were used to develop the FOSQ-10. Of the 30 original FOSQ items, 10 questions representing each of the 5 subscales were selected if they had a normal distribution of responses and the largest pre- to post-treatment effect size. The psychometric properties of the instrument were then evaluated with data from a second, independent sample of CPAP-treated OSA patients (n = 51 AH I = 51 +/- 28).
Results: Internal consistency of the FOSQ-10 was alpha = 0.87. Pre-treatment correlations of the 2 scales was r = 0.96. After 3 months of treatment the correlation was r = 0.97 (P < 0.0001). Subscales were also highly correlated at baseline and following treatment. Effect sizes for both instruments were highly correlated and indicated ability to measure meaningful change. Differences were observed between scores on the FOSQ-10 for normal controls and OSA patients.
Conclusions: The FOSQ-10 is a psychometrically strong instrument that performs similarly to the long version. The rapidly completed and easily scored FOSQ-10 shows promise for application in the clinical setting.