Validity and Reliability of Greek Version of Functional Outcomes of Sleep Questionnaire (FOSQ), Comparison of FOSQ with Questionnaires Measuring Sleepiness, Anxiety and Health Status

Background: We developed the Greek version of the Functional Outcomes of Sleep Questionnaire (G-FOSQ) and investigated its reliability and validity in Obstructive Sleep Apnea Syndrome (OSAS) patients. Methods: This is a prospective study, included all 311 consecutive adults, who visited sleep laboratory of a tertiary hospital for evaluation of suspected OSAS in a year period. Participants underwent standard polysomnography study and completed a battery of questionnaires including the Epworth Sleepiness Scale (ESS), Short Form-36 Health Survey (SF-36), and ZUNG Self-Rating Depression Scale (SDS). Results: A total 297 participants (72.4% men, mean age 52.9 ± 13 years, and body mass index (BMI) = 33.6 ± 7.2 kg/m2) who had OSAS were included. We assessed the internal consistency, factor analysis, multi-traits scaling analysis, and the concurrent validity of the G-FOSQ. Factor Cronbach’s alpha coefficient for all domains of FOSQ exceeded the 0.70 standard for internal consistency. Item domain correlations ranged from 0.37 to 0.90. The global G-FOSQ and the G-FOSQ subscales had medium-sized correlations (r = 0.30-0.5) with SF-36 subscales scores. We found excessive decreasing scores of G-FOSQ in patients with ESS > 11. When patients classified based on SDS, no differences were found on G-FOSQ, but there was a positive correlation with the Vigilance subscale and SDS, fact that until now has been shown in patients with Restless Legs Syndrome. Conclusions: The stability of structures and the liability of the questions of the G-FOSQ (0.913) was found to be similar the score of original FOSQ (0.94). The G-FOSQ is a reliable and valid instrument for assessing functional outcome in participants with daytime sleepiness in Greek population with OSA.


Introduction
Obstructive sleep apnea syndrome (OSAS) is one of the most disabling sleep disorders [1] and of a great impact on the daily functioning [2,3]. The Functional Outcomes of Sleep Questionnaire (FOSQ) is widely used measure of functional status resulting from sleepiness and has been effectively employed as a measure of sleep-related quality of life [4] and to assess the impact of known or suspected sleep disturbances on daytime function [5].
The purposes of this study were 1) To examine the factor structure of the Greek translated version (G-FOSQ) and 2) To examine its reliability and validity.

Methods
This is a prospective study, included all 311 adults,

Epworth sleepiness scale
The ESS [10] is a short-self-administered questionnaire that provides information on daily conditions of sleepiness [11]. Scores > 11 are generally considered positive for Excessive Daytime Sleepiness (EDS).

The zung self-rating depression scale (SDS)
The SDS [12] is a 20-item self-report assessment device built to measure anxiety levels, scoring: Cognitive, autonomic, motor, and central nervous system symptoms [13].

Statistical Analysis
Basal characteristics were described as mean ± standard deviation for quantitative variables. The Pearson correlation coefficient and level of significance were used to compare the questionnaires. Probability values of p < 0.05 were considered as statistically significant.
Internal consistency reliability was assessed using Cronbach's alpha [14] and test-retest reliability with an interclass correlation coefficient. Construct validity for the FOSQ subscales were assessed by comparing with the SF-36 scales. The software SPSS 21.0.0 (Chicago IL, USA) was used.

Results
During a year period of study, a PSG study was conducted in 311 individuals. We excluded 14 subjects: 3 who did not wish to complete the questionnaire, 9 who received psychiatric treatment, and 2 who had undergone a year's follow-up study. Eventually 297 people joined and evaluated: 215 (72.4%) men and 82 (27.6%) women. The mean age of the participants was 52.9 ± 13years (range 18-85 years) and the mean Body Mass Index (BMI) was 33.6 ± 7.2 kg/m 2 (range 20.5-62.5 kg/ m 2 ).

Structural construct validity
When assessed the test-retest reliability with an interclass coefficient to correlate the 5 sub-sections of the questionnaire with the questions that they consist, we found significant correlation ( Table 1). who visited sleep laboratory of a tertiary hospital for evaluation of suspected OSAS from January 2015 to December 2015.
The night before the Patients Underwent Standard Polysomnography (PSG), they completed a battery of questionnaires included FOSQ, Self Functioning Health Survey-36 (SF-36), Epworth Sleepiness Scale (ESS), and The Zung Self-Rating Depression Scale (SDS) in a private place, without any guidance. Explanations were given only as general guidelines by a nurse.
Demographic and medical history was recorded reviewing the medical records from the hospital data. The ethical committee approves the study as it was a non-interventional study.

Functional outcomes of sleep questionnaire
The FOSQ was specifically designed for measuring the impact that primary or secondary excessive sleepiness disorders have over daily functionality. It is a self-administered questionnaire [7] made out of 30 questions which constitute five subscales: 1) Activity level (9 items); 2) Vigilance (7 items); 3) Intimacy/sexual relationships (4 items); 4) General productivity (8 items) and social outcomes (2 items). Has a 4-point Likert response format (1 = extreme difficulty, 2 = moderate, 3 = little, 4 = no difficulty). Missing responses are not included in the score calculation. Subscale scores range from 1-4 with total scores ranging from 5-20, with higher scores indicating better functional status.

Self functioning health survey-36
The SF-36 Health Survey [8] is a 36 item self-administered questionnaire which assesses non-disease specific health-related quality of life, validated in Greek [9] and covering the domains: Mental health functioning (social functioning, role-emotional, vitality, mental health) and physical functioning (role-physical, bodily pain, general health, physical functioning).

Discriminate validity
Based on the AHI index, patients were divided into

Reliability
The coefficient-Alpha correlation ranged from 0.290-0.889, indicate substantial contribution of the questions to the final reliability (Table 2). For Social Outcome, Vigilance, Intimate/Sexual activity the coefficient-Alpha was particularly high (Alpha > 0.800)-indicating strong reliability. For General Productivity (Alpha = 0.764) and Activity Level subscales (Alpha = 0.731) the reliability was moderate to strong.

Achieving higher and lower floors (Floor and ceiling effects)
Almost uniform distribution of query values was ob- countries requires linguistic adaptation together with a re-examination of its validity. Several language versions of the FOSQ including Norwegian (N-FOSQ) [15], Spanish [16], Swedish (S-FOSQ) [17], Thai [18] and Korean [19] have been recently evaluated in patients with sleep disorders, especially with OSAS. The G-FOSQ has produced comparatively similar good results. The stability of structures and the liability of the G-FOSQ (0.913) was found to be similar to the global score (0.94) [4]. The fluctuations of individual subscales are also excellent (0.713-0.936) similar to K-FOSQ (0.80-0.94), N-FOSQ (0.66-0.96) [15] and Turkish versions (T-FOSQ) [20]. A tendency of FOSQ to show no correlation with the AHI scores, as described both in K-FOSQ [19] and Thai-FOSQ [18], was also found.
The confirmation that the FOSQ measures the effects of functional status has already been shown from Weaver, et al. [21] achieving the desired correlation with SIP [21] and SF-36 [8]. In accordance, we found moderate correlation with all subscales of SF-36. However, there was no correlation between intimacy/sexual activity (G-FOSQ) and the vitality (SF-36). The T-FOSQ [20] excluded this subscale because their patients found inappropriate answering these questions for religion reasons. Additionally, data showed [22] that patients over 65 years tend not to fill out these questions (30.4% filled in), therefore any correlation lack reliability. We are not excluding these questions from the G-FOSQ as the internal validity of the questions of this subscale (Q27-Q30) were high (r = 0.85-0.90, p = 0.001), which is the most important factor for this decision. Perhaps, the lack of correlation ought to racial mentality differentiation in the Greek population regarding the perception of vital-three severity groups of OSAS. Only the Vigilance subscale showed difference between moderate and severe OSAS patients (2.8 ± 1.1 vs. 2.4 ± 1.25, p = 0.04). Significant differences found in all G-FOSQ subscales between the two groups, with higher values observed in the group with ESS < 11 ( Table 4). Based on the SDS, our patients were classified into only the first two categories; normal subjects and patients suffered from low anxiety symptoms, but no differences were found between the G-FOSQ subscales.

Discussion
The application of the FOSQ in non-English speaking  ity and its harmonization with sexual activity. Gender, age, income, married out of love and being still in love with the partner were all significantly associated with sexual interest and behaviors in Greek people [23] but not any kind of chronic disease that they suffer. Only, in the Korean translation (K-FOSQ) the evaluation suggested that 5 questions had to be removed as unrelated to the overall reliability of the questionnaire.
The daily sleepiness is the key for subjective evaluation of OSAS severity. We found, in agreement with literature [16], excessive decreasing scores of G-FOSQ in patients with ESS > 11. As depression constitutes an important factor "statistical noise" analyzes questionnaires object the quality of life [24]. We found no correlation, but the vigilance subscale appeared positive correlation with SDS, fact that until now has been shown in patients with Restless Legs Syndrome [25].
In conclusion, the results from this study provide that the G-FOSQ is a reliable and valid instrument for assessing functional outcome in Greek Population with daytime sleepiness.