Objective: The Functional Outcomes of Sleep Questionnaire, FOSQ, is a self-administered 30 item questionnaire, designed to assess the impact of disorders of excessive sleepiness on activities of daily living. The aim was to evaluate the psychometric properties of a Swedish translation of the English original.
Materials and methods: A Swedish version of the FOSQ was answered by 75 consecutive patients, diagnosed with obstructive sleep apnea syndrome and in need of treatment. The Short Form Health Survey (SF-36) and Epworth Sleepiness Scale (ESS) were also answered at the same time to evaluate validity. The first 25 patients answered the FOSQ a second time, 3 weeks later, to assess reliability.
Results: The test-re-test reliability and intra-class correlation of the different sub-scales in the FOSQ varied between 0.71-0.92 and was 0.92 for the total scale, all statistically significant. Cronbach's alpha, calculated as a measure of internal consistency, varied between 0.84-0.92 for FOSQ sub-scales and was 0.96 for the total score. Statistically significant correlations between FOSQ sub-scales and the eight sub-scales in the SF-36 supported the validity. Discriminant validity, calculated by splitting responders with high and low ESS scores, revealed that FOSQs scores differed significantly between the groups.
Conclusions: The results suggest that the Swedish version of the FOSQ has psychometric qualities in line with the original. It might, therefore, be a potentially useful, reliable and valid instrument for clinicians and researchers when measuring variables related to quality-of-life in sleep disorders in this language area.