The average percentage of employees absent at any point in a calendar month, in the entire mine. The average percentage of employees absent at any point in a calendar month, in the entire mine. Data were collected for 33 consecutive months from November 1997 to July 2000. Period 1 covers the 8-hour/7-day roster, period 2 covers the 12-month period after the change to the 12-hour/7-day roster, and period 3 covers the 12-month period after some employees changed to the 12-hour/5-day roster. A Baker et al. Occup Environ Med 2003;60:43-49 ©2003 by BMJ Publishing Group Ltd