ABSTRACT
This chapter begins by noting that complex systems such as health-care delivery are composed of a series of hierarchically organized subsystems. It indicates some of the factors that are relevant, and what kinds of approaches will tend to produce safer systems. A human-machine system is usually thought of as something where there is a piece of equipment that the operator controls directly or through the use of an automatic controller. Local causes of error are usually more readily manageable than global causes, but there is a sense in which global causes, if they can be controlled, have greater payoffs, because the effect of action at a global level will be far more pervasive throughout the system than will local intervention. An important distinction in the errors of individuals is between slips, mistakes, and violations. Although errors are made by individuals, most work situations are such that a person is a member of a group or team either directly or indirectly.
