An Industrial Study of the Effects of Feedback and Fault Density on Inspection Performance

Records of the performance of a group of on-line inspectors of glass items over a ten month period were analysed using the Theory of Signal Detection. It was found that the inspection group as a whole followed the theoretical predictions. The introduction of more rapid feedback of performance to the inspectors after twelve weeks of the study increased the effective detectability of the faults significantly, reducing the percentage of missed faults by half. The effect of input quality level on performance before and after the change was studied. The usual drop in fault detection performance with increased quality was found and analysed to show that the inspection group were attempting to keep the outgoing percentage defective constant.