Abstract
The performance of twelve computer operators was measured in the field, on two new portable tests of reaction time, during the first night of the night shift at 0400 h and at the beginning day shift (0800 h), over three successive three-week comparisons. The results were: (i) mean reaction time increased significantly on the night shift as compared with the day: (ii) the adverse effect of the night shift was absent during the first comparison and became increasingly apparent on the second and third replications. These results: (i) provide evidence of inferior performance on the night as compared with the day shift in the field : (ii) show that data from previous studies of sleep deprivation in the laboratory are able to provide a good indication of what was to be expected in the field: (iii) emphasize the need for longitudinal studies in order to assess the true effects of stressful influences.