Unnoticed Effects of Inspection Errors and a Quality Paradox

Abstract

A central element of quality assurance is inspections. Inspections, however, are imperfect and prone to errors. Devastating effects of inspection error type I -rejection of conforming items, are considered in this note. When several inspections are performed along a serial process, the number of falsely rejected items is similar in magnitude to (or even larger than) the number of defective items. Moreover, to compensate for this loss, more units should enter the process and consequently, more units turn defective. The quality community seems to be unaware of these effects, certainly of the last one, despite their practical significance.

Quantifying the Impact of Inspection Processes on Production Lines through Stochastic Discrete-Event Simulation Modeling

“…Even then, such systems are not infallible, and inspection errors must be accounted for, increasing the difficulty of accurately estimating production output and quality of units processed. This is especially important as the number of defects increases with the number of units processed; hence additional production to account for quality issues accumulates non-conforming units [4]. Overall, inspection results can be considered as a stochastic variable too, where missed defective units and false rejections can be missed by the inspection system.…”