Psychometric evaluation of a Swedish version of the Functional Outcomes of Sleep Questionnaire, FOSQ

Abstract

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.