a method for evaluating the effectiveness of a person to perform a task based on his / her previous or predicted sleep activity is provided . the method can be used to predict changes in task effectiveness at any time of day , based upon numerous patterns of sleep and activity , either experienced or planned for the future . the method take into account progressive increases in sleep deprivation , the effects of the time of day on performance , and changes in the time when a person sleeps and works . the method also accounts for the quality of a sleep interval and a person &# 39 ; s sleep inertia , the temporary slowing of performance immediately after awakening . the method is homeostatic . gradual decreases in sleep debt decrease sleep intensity . progressive increases in sleep debt produced by extended periods of less than optimal levels of sleep lead to increased sleep intensity . as a result the method can predict the normal decline in sleep intensity during the sleep period and the normal equilibrium of performance under less than optimal schedules of sleep .