Study objective: Discrepancies between several widely used assessment tools suggest that subjective daytime sleepiness is not a unitary phenomenon. Most research, however, has been based on patients. The aim of this study was to examine whether qualitatively different facets of subjective daytime sleepiness exist in the general population and to assess how different aspects of subjective sleepiness varied by age, gender, education status, body mass index, sleep debt, Stanford Sleepiness Scale, and objectively measured sleepiness (Multiple Sleep Latency Test).
Design: Cross-sectional study.
Setting and participants: Population-based sample of 1562 women and 1351 men, mean age of 46.6 +/- 7.9 years, including a subset of 145 participants who underwent an Multiple Sleep Latency Test.
Measurements: Self-reported sleepiness problems, Epworth Sleepiness Scale items, sleep habits, Multiple Sleep Latency Test, and Stanford Sleepiness Scale.
Results: Principal-axis factor analysis of 13 self-reported daytime-sleepiness measures yielded 3 factors, labeled perceived daytime sleepiness (Cronbach's alpha = 0.74), subjective sleep propensity in active situations (alpha = 0.82), and subjective sleep propensity in passive situations (alpha = 0.63). The factor-based scores were all related to increased body mass index and lower education status, but the associations of scores for perceived and subjective propensity factors differed with gender, age, sleep debt, MSLT, and Stanford Sleepiness Scale. Worse perceived sleepiness factor-based score was significantly related to female gender, younger age, higher sleep debt, and worse Stanford Sleepiness Scale scores. Worse factor-based scores for subjective sleep propensity in both active and passive situations were significantly associated with male gender, older age, and worse Multiple Sleep Latency Test scores.
Conclusion: Findings from the present analysis on a general population sample support the hypothesis that subjective daytime sleepiness has multiple dimensions.