Analysis Techniques For Man-Machine Systems Design

NATO UNCLASSIFIED- 111 - AC/243(Panel-8)TR/7Volume 25.7 ERROR ANALYSISWhat the technique doesError analysis techniques are used to identify the most likely sources of operator error in a system, with a view totheir prevention through modification of the design, the operational procedures, or by training. The general approachto mission, function, and task analysis, outlined in previous sections of this chapter, provides a good basis for erroranalysis. Hammer (1972) discusses the use of mission and task analysis as the basis for hazard analysis and systemsafety. Fadier (1990) reviews a number of analytical techniques, including function block diagrams, flow graphs, andSADTrm as bases for error analysis. He notes that a number of approaches are based in value analysis. The techniqueRELIASEP, developed in France, is a typical example (Fadier, 1990).More specific techniques, such as Failure Modes Effects Analysis, are available for the detailed study of systemoperator error. Technique for Human Error Prediction (THERP) is an approach to error analysis which has beendeveloped and used over a twenty year period (Miller & Swain, 1987). The sequence of analyses used for THERPstarts with the a detailed task analysis, including analysis of performance requirements, followed by qualitativeperformance assessment to determine potential human errors, leading to a quantitative assessment of errorprobabilities using fault tree analyses, calculation of the probabilities of recovering from errors, and a calculation ofthe contribution of human error probability to system failure. THERP has been described in detail in the review ofhuman performance models reported by ACP/43 Panel-8/RSG.9 (McMillan etal., 1991). The technique is verylabour intensive, and will not be discussed further here.In less rigorous approaches than THERP. errors may be identified based on an analysis of operator tasks, and referenceto an error classification. Hammer (1972) provides a list of 34 "causes of primary errors" - both human factors (lackof attention) and human engineering (interference with normal habit pattems) - together with recommended designsolutions. Norman (1983) reports an analysis of one class of operator error and uses it to produce recommendationsfor the design of computer systems. Rouse (1990) provides a classification scheme for 31 types of error in operatingsystems. Reason (1987) proposes a Generic Error Modelling System (GEMS) which integrates approaches such asNorman's and Rouse's based on Rasmussen's (1983) categories of skill, rule, and knowledge based behaviour. To beapplied, these classifications of operator error must be related to the proposed operator tasks. Stoop (1990) reports theuse of normative task analysis and GEMS to identify potential errors in the operation of a ship's bridge. In thisapproach, the task analysis is elaborated to the required level of detail.and the generic error modelling system is thenapplied.The limitations of the classifications mentioned above are that they provide no information on the relativeprobabilities of operator error. Such approaches should involve the development of data bases of likely operatorerrors. With the exception of AIR Data Store (Munger, Smith, & Payne, 1962), few such data bases exist (seeMeister, 1985; Miller, 1987). Hale et al. (1987, 1989) report the development of a compuLer-based software tool forthe collection and analysis of data on accidents and near misses. Their Intelligent Safety Assistant (ISA) is intended tofacilitate the interactive collection of such data. More recently the US Coast Guard and the US Air Foree haveimplemented extensive accident reporting and analysis systems, aimed at identifying human engineering factors inaccidents.NATO UNCLASSIFIED- 111 -