Risk and effort measures of fatigue.

A method of measuring fatigue is suggested in which alternative routes, requiring different amounts of effort, lead to different probabilities of success or failure. An experiment designed to investigate a task which has these features shows it sensitive to the fatigue generated by a synthetic work battery. Fatigued Ss shifted their choices towards easier, riskier routes, compared with their own earlier performance and with that of a control group; they also showed an increased error rate on a subsidiary measure. In a second experiment, measurements on the task were shown to correlate with self-rated fatigue.