Slips and lapses

This chapter describes accidents caused by those slips and lapses of attention that even well-trained and well-motivated persons make from time to time. For example, they forget to close a valve or close the wrong valve. They know what they should do, want to do it, and are physically and mentally capable of doing it. But they forget to do it. Exhortation, punishment, or further training will have no effect. We must either accept an occasional error or change the work situation so as to remove the opportunities for error or to make errors less likely. 

Here we discuss the concepts of error and uncertainty. In the world the word error implies a failure of some kind—synonyms include mistake, blunder, slip, and lapse. In metrology, error is defined as the result of a measurement minus a true value of the measurand and is free of such negative connotations. Error in an analysis is a particular value that may be known if the true value is given. 

Slips and lapses often occur when the task being undertaken is overly complex or long-winded. Similarly we may be susceptible when we are dealing with steps... 

Products with suboptimal user interfaces can be difficult and expensive to fix once they are in live operation. Not only do changes need to be carefully implemented but training materials and user documentation are also likely to need a refresh. It is far more efficient to get the user interface right from the start. Similarly manufacturers need to have an appreciation that poor interface design cannot be realistically be remedied by additional training. As discussed in Sect. 2.6 most slips and lapses simply cannot be addressed through the provision of advice or guidelines. 

In Sect. 5.3.1 we discussed the concepts of slips and lapses and there are a number of design principles which can be employed to reduce the incidence of these. Slips for example can be addressed by avoiding common but not identical action sequences. Suppose viewing or cancelling an appointment requires an almost an identical series of mouse clicks. Should one of these activities be much more common than the other it is likely that from time to time an error will be made when actioning the infrequent task. Similarly buttons with unrecoverable consequences should be separated from more benign, frequently used functions. For example, it would be wise to design in some physical distance between buttons entitled Record patient death and Update patient address . 

Slips and lapses occur when a person knows what they want to do, but the action does not turn out as they intended. Slips relate to observable actions and are associated with attentional failures, whereas lapses are internal events and associated with failures of memory. Slips and lapses occur during the largely automatic performance of some routine task, usually in familiar surroundings. They are almost invariably associated with some form of distraction, either from the person s surrounding or their own preoccupation with something in mind. When Charles Darwin went to the wrong tea caddy, he had a lapse of memory. If, on the other hand, he had remembered where the tea was but had been momentarily distracted and knocked the caddy over rather than opening it, he would have made a slip. 

Reason divided error into slips, or lapses, and mistakes. Slips or lapses involve the correct choice of a method to achieve a task, but a failure to carry it out correctly. Mistakes on the other hand involve a flaw in the plan which means that even if it is carried out correctly, the objective isn t achieved. Slips and lapses are often skill-and rale-based errors, whereas mistakes are often knowledge-based errors. 

Skill- and rale-based decisions are the basis of routine activities. As a result, there are more absolute numbers of errors in such decisions, but the percentage of errors is much lower than in knowledge-based decisions. The types of errors in activities based on skill- and rale-based decisions are more likely to be what are called slips and lapses . Slips come from attentional failure, lapses from memory failure - they are two types of unintended actions. The types of errors in knowledge-based decisions are more likely to be what are distinguished as mistakes - errors in planning a path to an outcome. Mistakes are a type of intended action, and may be rule-based or knowledge-based. They occur when the selection of an objective and the means to achieve it are faulty, whether or not the actions go as planned. 

Slips and lapses are examples of skill-based errors. A slip can be defined as a failure of attention, in which an action may not be completed as intended. A lapse can be defined as a failure of memory, where an intended action is forgotten and not carried out. This may be due to the operator being intermpted at their task. 

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