Errors may be further categorized as judgment errors (improper selection of an objective or a plan of action), execution errors (proper plan carried out improperly), errors of omission (when something that should be done is not done), and errors of commission (when something that should not be done is done) (IOM 2000; Reason 1990). Active errors are those committed by frontline workers; the results of active errors are usually seen immediately (Reason 1990, 1997). For example, the CNAs in the nursing care home event described at the start of this chapter experienced an active error when the lift collapsed during a resident transfer. Latent errors, on the other hand, occur in the upper levels of the organizationin this instance, failing to secure adequate resident care equipment in the nursing care home. The error may lie dormant for days or years until a particular combination of circumstances allows the latent error to become an adverse event (Reason 1990, 1997). Violations may also be further categorized as routine, optimizing, and situation. Routine violations may be thought of as activities that cut corners. Optimizing violations are "actions taken to further personal rather than task related goals" (Reason 1995, 82). Situation violations occur when a person believes that the action "offers the only path available to getting the job done and where the rules or procedures are seen as inappropriate for the present situation" (Reason 1995, 82). The distinction between errors and violations is important to managers because they have different contributing causes and, in turn, require different solutions, as summarized in exhibit 13.1. Finally, Reason's Swiss cheese model assumes a collection of defenses that act as buffers or safeguards to prevent a hazardous situation from becoming an adverse event, just as a thick oven mitt would prevent a restaurant worker from dropping a hot dish. The collection of defenses in an organization may be thought of as several slices of Swiss cheese lined up next to each other. The holes in the slices represent the latent and active errors present in the organiza-tion. Even if an error may be present (i.e., a hole in one slice), it often does not result in an adverse event or accident because there are organizational defenses to stop it from continuing (i.e., the next slice). An example of an organizational defense is the standard practice of having a pharmacist review the appropriate-ness of all physician orders for medications to be dispensed. A physician may inadvertently write an incorrect dosage; however, when the pharmacist picks up the mistake and clarifies the order with the physician (organizational defense), a medical error (and potential adverse event) is prevented.

Exercise 13.1 from the text: Consider the scenario described in the exercise. Using- the table provided in the exercise, list the errors and risk factors into the appropriate categories.