To examine the relationship of overtime and extended work shifts on health and safety, 52 research studies were classified under four categories, based on the information contained in the reports:

1. Overtime: most studies compared the number of hours worked by full-time participants and reported no other work schedule details.
2. Extended work shifts: 10- or 12-hour shifts were compared with 8-hour shifts in most studies and used a standard 40-hour work week. Some studies, however, did not clearly report the number of hours worked per week. Some studies, however, did not clearly report the number of hours worked per week.
3. Extended work shifts combined with more than 40 hours per week: 12-hour shifts compared with 8-hour shifts in most studies.
4. Very long shifts (e.g., resident physician on 32-hour call schedule and 48-hour taxi driver schedule).

The process of classifying the studies into these categories often was hampered by lack of a complete and clear description of the work schedules. For example, the studies examining 12-hour work shifts did not always clearly report the number of hours worked per week. Thus, some misclassification of studies is possible in this summary document. In addition, the complexity and wide variety of work schedules studied made it difficult to compare and synthesize findings across the 52 reports.

Work schedules differ in many ways, and more than 10,000 schedules are in use worldwide [Knauth 1998]. Time of work (day, evening, night), fixed or rotating shift, the degree of worker control over work times, number of hours worked per day, number of consecutive workdays before rest days, number of hours worked per week, number of rest days, and number of weekends off were all factors that combined in a variety of ways across these field studies. An individual study’s finding for shift length or number of hours worked per week may have been influenced by time of work or other characteristics of the work schedule. Thus, some caution should be exercised in characterizing some of these studies or interpreting their findings solely in terms of long hours of work or extended shifts.

Tables 1 and 2 list the country where the studies were conducted and the type of work. Approximately 20% of the studies were conducted in the United States, 28% in Asia, and 35% in Europe. The studies were conducted in field settings, except for three laboratory investigations. The most frequent types of work studied were health care, white collar, and manufacturing. The age groups studied ranged from young adults to older workers in their 60s, but only two studies specifically addressed the relationship of age to health effects. Men were examined exclusively in 40% of the studies, as compared with 10% of studies that examined only women.

Work schedules differ in many ways, and more than 10,000 schedules are in use worldwide.

[Knauth 1998]

Index: Main Page Table 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7 Table 8 Table 9 Abbreviations Acknowledgments Introduction Description of Work Schedules and Samples Health and Safety Findings Summary Concluding Remarks References