A Meta-Analysis on Work Schedule Characteristics and Sleepiness

Introduction: Atypical working hours, including shift work as well as work during weekends, evenings, and nights, are known to be risk factors for workers’ health and safety. Fatigue, including sleepiness, is considered a key factor mediating these effects. Given this central role of sleepiness, many studies have investigated how it is affected by different aspects of working hours or work schedules. However, the empirical evidence is mixed and difficult to generalize, since many studies have focused on specific shift systems within particular organizations or occupational groups. Therefore, to better understand the relationships between work schedule characteristics and sleepiness, this study aims to meta-analytically synthesize research on these relationships. Specifically, we examine how sleepiness changes with (1) shift length, i.e., time into shift, (2) shift type (e.g., day versus night), and (3) number of consecutive shifts.

Methods: This review is part of a broader project examining the relationships between different aspects of working hours and fatigue as well as need for recovery. In this broader project, we conducted a systematic literature search of peer-reviewed publications in various databases in February 2024, which yielded 16,804 hits. After removing duplicates, 9,168 abstracts and 805 full texts were screened. We updated the search in January 2025, and after removing duplicates, a further 744 hits were screened. This part of the study focuses on original studies examining sleepiness measured with the Karolinska Sleepiness Scale. Statistical analyses are in progress. We plan to calculate mean overall effect sizes (Hedges’ g) comparing sleepiness for (1) different lengths of time into shift, (2) different shift types, and (3) different numbers of consecutive shifts using random-effects models.

Results: We included 38 studies on time into shift, 31 studies on shift type, and 13 studies on the number of consecutive shifts in the meta-analyses. Most of these studies used repeated measures design and had small samples, often less than 100 participants. Nurses were the most frequently studied occupational group. As expected, preliminary results indicate that sleepiness is higher during night shifts than during day shifts. However, results regarding time into shift and number of consecutive shifts are less clear. The final results will be presented at the symposium.

Conclusion: This review provides a comprehensive and up-to-date overview of research on work schedule characteristics and sleepiness, enhancing the understanding of these relationships. Besides, its findings will support the evidence-based design of work schedules that reduce the risk of worker fatigue in the short term, while contributing to reduced health and safety problems in the long term.

Publikationsverlauf

Artikel online veröffentlicht:
08. Oktober 2025