Looking for errors of omission and commission or The Hunting of the Snark revisited

Since the early 1990s, considerable effort has been spent to understand wha t is meant by an "error of commission" (EOC), to complement the traditional notion of an "error of omission" (EOO). This paper argues that the EOO-EOC dyad, as an artefact of the PSA event tree, is insufficient for human reli ability analysis (HRA) for several reasons: (1) EOO-EOC fail to distinguish between manifestation and cause; (2) EOO-EOC refer to classes of incorrect actions rather than to specific instances; (3) there is no unique way of c lassifying an event using EOO-EOC: (4) the set of error modes that cannot r easonably be classified as EOO is too diverse to fit into any single catego ry of its own. Since the use of EOO-EOC lends to serious problems for HRA, an alternative is required. This can be found in the concept of error modes , which has a long history in risk analysis. A specific system for error mo de prediction was tested in a simulator experiment. The analysis of the res ults showed that error modes could be qualitatively predicted with sufficie nt accuracy (68% correct) to propose this method as a way to determine how operator actions can fail in PSA-cum-HRA. Although this still leaves the th orny issue of quantification, a consistent prediction of error modes provid es a better starting point for determining probabilities than the EOO-EOC d yad. It also opens a possibility for quantification methods where the influ ence of the common performance conditions is prior to and more important th an individual failure rates. (C) 2000 Published by Elsevier Science Ltd. Al l rights reserved.