The Psychology of Human Error

While the consequences of medical errors can be devastating, in reality, medical errors are not unique. Medical errors are simply errors in a medical context. As such, we can turn to what we know about the nature of human error in general to understand why medical errors occur, what factors produce them, and how to design to reduce them.

Slips, Lapses and Mistakes

Cognitive psychologists distinguish between “skill-based” performance, “rule-based” performance, and “knowledge-based” performance. Skills are highly practiced behaviors that we perform routinely, with little conscious effort. They’re literally automatic. Rule and knowledge-based performance require more mental involvement or conscious deliberation. We rely on them when skill-based performance won’t work, typically in exceptional or novel situations.

Slips and lapses are errors in the performance of skill-based behaviors, typically when our attention is diverted. A common mechanism for a slip is “capture”, in which a more frequently performed behavior “takes-over” a similar, but less familiar one. For example, a capture error is made when a nurse misprograms a new infusion pump because the sequence of steps is similar, but not identical to the pump he is most familiar with. Description errors are slips that occur when the objects of different actions are close together or visually similar, as when the wrong control on an EKG is adjusted because it’s close to other controls that look the same. Loss of activation errors are lapses where the goal is forgotten in the middle of a sequence of actions (e.g., a radiologists forgetting what he is looking for after retrieving and displaying a comparison study), or we omit a step in a routine sequence (e.g., the failure to complete a “double-check” for blood-type in an organ transfer protocol).

Slips and lapses occur while our attention is diverted and we fail to monitor the actions we’re performing.

Mistakes are errors in rule or knowledge-based performance. They arise when we misinterpret a situation or misapply a rule (usually, a rule that is frequently used and seems to fit the situation well enough). Mistakes include errors in perception, judgment, inference, and interpretation. Mode errors are common mistakes. A mode error arises when we perform an action appropriate for one mode, but we are mistakenly in another (e.g., when a nurse assumes the default analgesic concentration of 1.0 mg applies, but the pump was set to 10 mg by previous user). Misdiagnoses, misinterpretation of test results, failing to provide indicated prophylactics, and failing to respond to a device alarm are all examples of mistakes.

The Role of Attention

As with slips and lapses, attention plays a key role in mistakes. Whereas attention’s job is to monitor skill-based performance, our attention is actively engaged in the analytical reasoning and problems solving of rule and knowledge-based performance. As a result, slips, lapses, and mistakes are all more common when situational factors divert our attention. Situational factors include physiological factors like fatigue, sleep loss, alcohol, drugs and illness and psychological factors such as having to juggle multiple activities, stress, boredom, frustration, fear, anxiety, and anger.

Two Sides of the Same Coin

Errors are a predictable consequence of basic and normally useful cognitive mechanisms, not random or arbitrary processes. As error expert James Reason suggests, correct performance and systematic errors are two sides of the same coin.