schedule while ensuring that shifts are optimally filled, in contrast to the generally poor human outcomes of fatigue, stress, estrangement with friends and family and health problems that have been reported with algorithm-based scheduling of work-shifts. Mental (cognitive) fatigue due to inadequate sleep an/or disturbances of circadian rhythms is a common contributor to accidents and untoward incidents. While the this risk cannot be eliminated, it can be managed through personal and administrative controls. This type of management is conducted through a Fatigue Risk Management System (FRMS). One method used within an FRMS is objective fatigue modeling to predict periods of high risk within a 24-hour shift plan. Modeling is accomplished with tools such as the Fatigue Avoidance Scheduling Tool (FAST) and the FAID Quantum Software Missing income is also a large part of shift worker. Several companies run twenty-four hour shifts. Most of the work is done during the day. When the work dries up, it usually is the second and third shift workers who pay the price. They are told to punch out early or use paid time off if they have any to make up the difference in their paychecks. That practice costs the average worker $92.00 a month. Medications Melatonin may increase sleep length during both daytime and nighttime sleep in people who work night shifts. Zopiclone has also been investigated as a potential treatment, but it is unclear if it is effective in increasing daytime sleep time in shift workers. There are, however, no reports of adverse effects. Modafinil and R-modafinil are useful to improve alertness and reduce sleepiness in shift workers. Modafinil has a low risk of abuse compared to other similar agents. However, 10% more participants reported adverse effects (nausea and headache) while taking modafinil. In post-marketing surveillance, modafinil was associated with Stevens–Johnson syndrome. The European Medicines Agency withdrew the license for modafinil for shift workers for the European market because it judged that the benefits did not outweigh the adverse effects. Using caffeine and naps before night shifts can decrease sleepiness. Caffeine has also been shown to reduce errors made by shift workers. Epidemiology According to data from the National Health Interview Survey and the Occupational Health Supplement, 27% of all U.S. workers in 2015 worked an alternative shift (not a regular day shift) and 7% frequently worked a night shift. Prevalence rates were higher for workers aged 18–29 compared to other ages.