Understanding Human Performance and Error

The analysis of accidents and disasters in real systems makes it clear that it is not sufficient to consider error and its effects purely from the perspective of individual human failures. Major accidents are almost always the result of multiple errors or combinations of single errors with preexisting vulnerable conditions (Wagenaar et al., 1990). Another perspective from which to define errors is in terms of when in the system life cycle they occur. In the following discussion of the definitions of human error, the initial focus will be from the engineering and the accident analysis perspective. More detailed consideration of the definitions of error will be deferred to later sections in this chapter where the various error models will be described in detail (see Sections 5 and 6). 

From a reliability engineering perspective, error can be defined by analogy with hardware reliability as The likelihood that the human fails to provide a required system function when called upon to provide that fimction, within a required time period (Meister, 1966). This definition does not contain any references to why the error occurred, but instead focuses on the consequences of the error for the system (loss or unavailability of a required function). The disadvantage of such a definition is that it fails to consider the wide range of other actions that the human might make, which may have other safety implications for the system, as well as not achieving the required function. 

Meister (1977) classified errors into four major groupings  

This classification underscores the inadequacy of the approach common in reliability engineering of simply classifying errors into omission and commission categories. 

An additional category related to the above was suggested by A. D. Swain  

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Chapter 2, Understanding Human Performance and Error, provides a comprehensive overview of the main approaches that have been applied to analyze, predict, and reduce human error. This chapter provides the reader with the vmderlying theories of human error that are needed to xmderstand and apply a systems approach to its reduction. 

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