Do ‘Sleepy’ and ‘Tired’ Go Together? Rasch Analysis of the Relationships between Sleepiness, Fatigue and Nonrestorative Sleep Complaints in a Nonclinical Population Sample

Abstract

Objective: The lack of distinction in the clinical use of terms like fatigue and sleepiness is an important issue. While both fatigue and sleepiness can potentially be associated with nonrestorative sleep (NRS) complaints, their relationships are still poorly described. We propose to use Rasch analysis-based methods to study the interrelations of fatigue, sleepiness and NRS. Methods: 150 subjects (mean age = 39.3 years, range = 18–65) from a community sample underwent a structured computer-assisted web interview. We assessed demographic data, sleep habits, and subjective fatigue with the Fatigue Severity Scale (FSS), global and situational sleepiness with the Epworth Sleepiness (ESS) and the Stanford Sleepiness Scales, respectively, and affective symptoms with the Hospital Anxiety and Depression Scale. Dimensionality, measurement invariance and common person equating were investigated to study the FSS, ESS and their relations to NRS. Results: NRS was linked to shorter habitual sleep duration and to higher scores on psychometric scales. Both sleepiness and daytime fatigue were positively correlated to each other and to the intensity of affective symptoms. Rasch analyses showed both the ESS and FSS to measure unidimensional concepts of sleepiness and fatigue, respectively. In contrast to the FSS, the ESS only showed partial invariance to an NRS complaint. Common person equating suggests that, despite similar Rasch-derived agreeability scores, fatigue and sleepiness (as measured by the FSS and ESS) nevertheless designate distinct constructs. Conclusion: NRS complaints can simultaneously present with higher daytime fatigue and sleepiness levels but the associative relationships between fatigue and sleepiness remain relatively unaffected by NRS. Although participants might not present adequate differentiation, fatigue and sleepiness seem to relate to different underlying concepts.

While Isolated Periodic Limb Movement Disorder Significantly Impacts Sleep Depth and Efficiency, Co-Morbid Restless Leg Syndrome Mainly Exacerbates Perceived Sleep Quality

“…It has been used in many studies investigating fatigue in several chronic conditions and in general population samples [43,44]. It is a 9-item, 7-point Likert type scale ranging from “completely disagree” (=1) to “completely agree” (=7).…”

“…Scores are usually reported as “mean scores” (ranging from 1 to 7) obtained by dividing the total score (ranging from 7 to 63) by 9. The most often proposed cut-off point on mean scores has firstly been 4 [45] and more recently 5 [43,44]. …”

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Correlates of residual fatigue in patients with major depressive disorder: The role of psychotropic medication

“…Previous studies have suggested that fatigue and sleepiness are two independent concepts (Shekleton et al, 2010). In both clinical and non-clinical populations, the association between fatigue and sleepiness was found to be weak (Anderson et al, 2003;Hossain et al, 2005;Neu et al, 2010Neu et al, , 2008. For example, in a study of 283 sleep-disordered patients, the Pearson's correlation between fatigue and sleepiness was 0.18.…”