Although the effects of sleepiness and fatigue has been extensively researched, the multi-layered, complex construct of fatigue has resulted in much of the research, particularly field-based studies, being confounded to some extent due to the many endogenous and exogenous variables that “interplay” simultaneously. As a result, there is still no universally accepted and agreed definition for fatigue or how to objectively measure fatigue per se other than for the effects of sleepiness and fatigue that, in turn, can negatively affect cognitive function.
A number of major industrial disasters such as Exxon Valdez, Chernobyl, Space Shuttle Challenger, Bhopal and three Mile Island occurred as a result of impaired cognition that were attributed, at least in part, to sleep deprivation and fatigue.