Diagnosis of Multiple Faults in Systems: Effects of Fault Difficulty,Expectancy,and Prior Exposure

Abstract

It has often been noted that today's human operators of complex industrial systems must occasionally deal with multiple component failures, but that they are trained instead to think in terms of single faults. This can lead to the minor inconvenience of simply taking longer to troubleshoot, or to the major hazards of a fundamental misunderstanding of system state. In two studies we examined these influences on subjects' ability to diagnose a multiple fault in a simulated electronic circuit: (1) objective multiple fault difficulty, (2) prior practice with multiple faults, and (3) expectancy or mental set for multiple faults. Previous research had confounded the latter two variables. Experiment 1 showed that the difficulty of multiple faults varied as our model predicted, but that the difficulty of certain faults interacted with verbalization. Experiment 2 showed that both prior practice and expectancy influence how effectively subjects deal with a difficult multiple fault, but not quite as expected. We conclude that the ability to diagnose multiple faults is multiply determined, depending on degree of practice, mental set, and the difficulty of the multiple fault itself. These results will help us define the requirements for decision support tools and they have also led us to perform investigations in the field, as reported in Reising and Sanderson (1995).