We all know that our jobs can be a source of stress. Forty percent of North Americans say their work is stressful. Stress can lead to physical symptoms like high blood pressure, increased heart rate, high cholesterol and weak immune systems. Our minds take a beating from stress as well. Mood disturbances, psychosomatic illnesses, depressive symptoms and total burnout can be caused by stress.
But what about performance? Does stress change how we perform our jobs? You bet it does. When you become stressed, your attention narrows and focusses on what seems to be important at the time. This means you may focus on a single task or only on the most salient cues for a few tasks while omitting other important tasks and cues.
Stress can also impair the capacity of your working memory. This reduces the amount and speed of information processing and means that it will take you longer to complete your work with the same high quality. If you try to get the work done in the same amount of time, you will make mistakes.
Fatigue results in some performance impairments similar to those resulting from stress. This means that when you are stressed and fatigued, your reduced attention and working memory abilities can be even worse than when you are suffering from one or the other alone[2,3]. It also means that you are even more likely to make mistakes.
Keep the effects of stress, and the similarities with fatigue, in mind when you are trying to improve performance or understand the causes of an accident or incident. The fixes for stress and fatigue are different. Stress might be reduced by changes to workloads, while fatigue might be reduced by changes to shift schedules. It will be important to know which one, or if both, are playing a role.
 Increased bodily arousal due to influences such as stress, can narrow attention and reduce the range of peripheral cues used. See for examples:
A – Easterbrook, J. (1959). The effect of emotion on cue utilization and the organization of behavior. Psychological Review, 66, 183-201.
B – Kahneman, D. (1973). Attention and effort. Prentice-Hall: Englewood Cliffs.
 High workload can exacerbate performance decrements due to fatigue and lead to an unwanted incident. See for example: Parker, A. & Hubinger, L. (1998). On tour analysis of the work and rest patterns of Great Barrier Reef pilots: Implications for fatigue management. Canberra: Australian Marine Safety Authority.
 The interaction of stress and fatigue may increase the risk of marine pilots exhibiting fatigue induced performance decrements. See for example: Parker, A., Hubinger, L., Green, S., Boyd, R., and Briggs, L. (1998). An Analysis of the Work Schedule of Great Barrier Reef Pilots. Canberra: Australian Maritime Safety Authority.