3 (1977) 165-182. A survey of the different types of shift-work systems in use, and the incidence of shift work in different industries and countries, is followed by a discussion of (a) the effects of shift work on health and (b) the physiological problems raised by the phase-shifting of the circadian cycle in night workers. Summaries of the existing knowledge of the effects of shift work on performance efficiency, accidents, and family and social life are then given, and a set of criteria for designing optimal shift systems is proposed. Next, the questions of selection for shift work and the provision of health services for shiftworkers are discussed. Finally, the need for further research on the problems of shift work is explained, and suggestions are offered on the lines such research should follow.Key words: accidents, attitudes, circadian r'hythms, gastrointestinal disease, interpersonal relationships, performance efficiency, personnel selection, psychosocial factors, shift work, sleep.The literature on shift work is ,considerable. Most of the available reports ,concern a particula'r approach to the problem. However, a more general view is given in some recent publications (22, 52,68,73, 90), and several international symposia have been devoted to this subject (e.g., 24, 27, 93, 94). 'I1he present paper is a review of the most important and generally a,ccepted facts on shift work and its possible effects on health and related factors.Institute of Work Physiology at the Univel'sity of Dortmund, Federal Republic of Gel'many.

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The safety of a ship depends substantially on its bridge watchkeepers, whose alertness and efficiency must be maintained at all hours of the day and night. Fatigue, circadian rhythms, and sleep disruption occasioned by the unusual working hours of these personnel may all affect their performance. A methodology for assessing the magnitude of this problem is proposed. The application of this methodology in a large-scale shipboard study of merchant mariners on extended voyages is then described, and details given of the techniques used to measure sleep and activity, and temporal variations in a range of physiological und psychological parameters. A summary of the data collected in the study is provided as a reference point for the reports on the different aspects of the results that follow in subsequent articles.

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A trial of an alternative to the traditional 4-on/8-off watchkeeping system was made on a container ship during a round trip from Europe to the Far East. The three navigating officers on the ship operated the new system, which involved "compressed" working hours with a long unbroken period of rest, during two sections of the voyage, one of which included six stops at ports. Despite unforeseen problems arising mainly from these stops, questionnaire responses concerning the new system were not altogether unfavourable to it, and daily records kept by the officers gave some support to the hypothesis that sleep would be better than under the traditional system. However, a number of difficulties were encountered; these are discussed in relation to the design of future studies of alternative watchkeeping systems.