Circadian rhythms in human performance.

Circadian rhythms in performance exist for a wide range of tasks studied under laboratory conditions; they also occur in measures of efficiency obtained in real-life situations. The rhythms appear to be related to the daily cycle of sleep "need", and the largest negative variations in performance are normally observed when this need is greatest. The detailed forms of the circadian functions are influenced to some extent by individual differences in age and personality. However, task factors are of equal, if not greater, importance in determining the nature of a performance rhythm, since its basic phase is markedly different in cases involving memory. This latter finding raises the practical problem of job design in relation to time of day, and a taxonomic approach is suggested as the most fruitful way of arriving at the optimal solution for particular work situations requiring different abilities.