Subjective and objective assessments after a change from a 4-crew, 12-h shift to a 3-crew, 12-h shift schedule: an observational study.

Abstract

To clarify the subjective and objective impacts of a change in a 12-h shift schedule, involving a reduction in the number of crews, on workers at an electronic parts production company. Forty-two workers participated in this study. Subjective indicators (e.g. questionnaires) and objective indicators [e.g., psychomotor vigilance task (PVT)], as well as an activity monitor-based sleep assessment, were measured during a > 1-year period that encompassed the shift schedule change. The study outcome was a comparison of work-related injury rates measured 1year before and after the change in shift schedule. After the shift schedule change, questionnaire scores regarding work-related burdens and PVT performance parameters, including mean response time and number of lapses, increased significantly. However, we also observed divergences in the trends of the subjective and objective measures 1year after the change. Despite these variations in both types of measures, we observed no significant differences in work-related injury rates measured before and after the shift schedule change. This study revealed that a reduction in the number of crews in a 12-h shift schedule has a negative impact on the subjective and objective indicator after the change in shift schedule; only indicators of alertness did not recover at 1year after the change. Assessments of the workers' performances and the regular implementation of health and safety programs for more than 1year are needed to maintain workers' health after the change in shift schedule.