Train and bus drivers, doctors and carers, employees in companies where machines run around the clock: In many industries, people work in shifts. Some start early in the morning, or at midday. Others ...

The standard workday runs from 9 a.m. to 5 p.m. Those who work other hours are engaged in “shift work”—starting before 7 a.m., ending after 6 p.m., and especially working overnight or a mixture of ...