Data was analyzed using IBM Statistical Package for the Social Sciences (SPSS), version 21.0 (IBM, Chicago, IL). Descriptive statistics such as means and standard deviation, mean ± SD, were used to describe the continuous variables. Frequencies and percentages, n(%), were used to describe the categorical variables. Associations between the presence of EDS, ISI, RLS, and demographic characteristics were examined using Chi-square tests. A p-value < 0.05 was considered statistically significant. Internal consistency of each of the three sleep questionnaires was investigated using Cronbach’s alpha (a) coefficient. Exploratory factor analysis with varimax rotation was used to examine whether the single-factor/component structure exists for each scale by retaining components with eigenvalues > 1.
The distribution of demographic factors and the presence of sleep disturbance is described in Table 1. The mean age for the entire sample was 29.8 (SD, 7.4), range 18-60 years. Males accounted for 75% of the overall sample, 85.9% had university degrees, 42.1% were unemployed, and 58.6% were single. Only 7.6% were smokers, 41% were coffee consumers, while 30.1% were tea consumers. In the study sample, the presence of excessive daytime sleepiness (ESS scores >10) was 48.5%. Also the presence of insomnia was 32.8% and RLS was 28.2%. The three sleep questionnaires demonstrated high internal consistency with Cronbach’s alpha values ranging between 0.84 and 0.94. Item analysis showed high internal consistency within the ESS questionnaire (Cronbach’s alpha = 0.84), the insomnia questionnaire (Cronbach’s alpha = 0.87), and the RLS questionnaire (Cronbach’s alpha = 0.94). The distribution of demographic characteristics and risk factors for EDS, ISI, or RLS is described in Table 1. The presence of EDS, ISI, and RLS was similar among gender groups, educational levels, marital status, smoke status, and coffee intake (p-value < 0.05). However, EDS was reported by 27.8% of tea drinkers compared to 56.3% of non-tea drinkers (p-value = 0.039). RLS was reported by 52.6% of tea drinkers compared to 19.2% of non-tea drinkers (p-value = 0.006).
Factor analysis of item scores showed that the insomnia scale had a single-factor structure with 65.7% total variance explained (Table 2). The factor loadings for the insomnia scale ranged from 0.64 “wake up too early” to 0.89 “sleep loss affects your mood.” Also the factor analysis showed a single-factor structure for the RLS scale with 84.2% total variance explained (Table 3). The factors loading ranged from 0.801 ” . . . unpleasant sensations are worse in the evening or at night than during the day, or only occur in the evening or night” to 0.965″ . . . unpleasant sensations are . . . totally relieved by movement.” Table 4 displays the structure of the Epworth Sleepiness Scale, as well as the factor loadings. In terms of the ESS, the factor analysis showed a two factor structure that accounted for 64.5% of the variance. Factor one accounted for 48.4% of the variance. It consists of five items reflected mainly on the chances of falling asleep when engaged in activities with a low somnificity, and the factor loadings ranged from 0.729 “lying down to rest in the afternoon when circumstances permit” to 0.868 “sitting and reading.” Factor two accounted for 16.1% of the variance, it consists of three items reflected mainly on the chances of falling asleep when engaged in activities with high somnificity, and the factor loadings ranged from 0.709 “in a car, while stopped for a few minutes in traffic” to 0.811 “sitting quietly after lunch.”