When there is a failure in a system where the human is a component, a strong tendency exists to blame the human. The easier way is to conclude that the system failed because the human made an error. This is a predisposition often shared by engineers, marketing people, juries in courts, and, unfortunately, sometimes people whose work is concerned with safety. Even today, when an airplane crashes, it is not uncommon to hear the news media focusing on the question or issue "What did the pilot do wrong?"
We humans do make errors. But, clearly, there are more productive approaches to dealing with system failures than focusing blame on the human component. In recent years, our team has conducted extensive theoretical and empirical research and experimentation on human error. Error is taken as a generic term that encompasses all those occasions in which a planned sequence of mental or physical activities fails to achieve its intended outcome, and when these failures cannot be attributed to the intervention of some chance agency." (Reason, 2004).
We recently had an opportunity to work on a project with a Fotune 500 company to stratify the data contained in a database related to safety incidents and accidents. The vast majority of the reports examined attributed fault to the person who was injured. "He or she was not paying attention" and "Human Error" were the most common phrases. Usually, there was little or no effort to consider the role of other potential factors such as the equipment being used, the environment in which it happened, the task that was being carried out, or how these aspects of the system fit or did not fit the person. Here again, there is often a tendency to assume the primary fault for an accident and injury lies with the employee.
A classification scheme for human error essentially starts with the concept of intention. Consider three alternatives:
Alternative 1 - A person intends to carry out an action, does so correctly, the action is appropriate, and the desired goal is achieved. No error has occurred.
Alternative 2 - A person intends to carry out an action, does so correctly, the action is inappropriate, and the desired goal is not achieved. An error has occurred.
Alternative 3 - A person intends to carry out an action, the action is appropriate, does it incorrectly, and the desired goal is not achieved. An error has occurred.
Consider alternatives 2 and 3, situations where errors occurred. They differ in an important respect. In alternative 2, the person did what he/she intended to do, but it did not work. The intention or plan or rule was wrong. This type of error is referred to as a mistake. The definition of a mistake is:
"Mistakes may be defined as deficiencies or failures in the judgmental and/or inferential processes involved in the selection of an objective or in the specification of the means to achieve it." (Reason, p. 9) In short, the person intended to do the wrong thing. In alternative 3, on the other hand, the person's intentions were correct, but the execution of the action was flawed - done incorrectly, or not done at all. This distinction between being done incorrectly or not at all is another important distinction. When the appropriate action is carried out incorrectly, the error is classified as a slip. When the action is simply omitted or not carried out, the error is termed a lapse.
"Slips and lapses are errors which result from some failure in the execution and/or storage stage of an action sequence." An important point can now be made about the origin of slips, lapses and mistakes. Slips relate to observable actions and are commonly associated with attention or perceptual failures. Lapses are more internal events and generally involve failures of memory. Mistakes are failures at a higher level - with the mental processes involved in assessing the available information, planning, formulating intentions, and judging the likely consequences of the planned actions.
The above distinctions have significant implications as to how one addresses the various types of errors; that is, how one tries to prevent or correct them. Slips are dealt with by addressing attention issues: using good displays, minimizing distractions, and so forth. Lapses are addressed by using memory aids, minimizing time delays, etc. Mistakes are dealt with by training, better procedural aids, etc. This theoretical framework offers us a way of thinking about and analyzing systems involving humans from a human cognition point of view. They give us guidance about the cognitive characteristics, abilities and limitations of people that have implications not just about what kinds of errors might be made, but also some suggestions about how to design systems so as to prevent them.
Blaming will be a counter-productive strategy, for real contributors to error are typically systemic in nature. Not only that, but an overuse of that strategy is the core building block of a culture of fear, and therefore, of lack of learning and innovation.
Copyright 2011 QBS, Inc.