Lot Acceptance Under Inspection Errors: Benefits of Multiple-Inspector Sampling Versus Single-Inspector 100% Inspection

In high-value and safety-critical manufacturing contexts (e.g., aerospace, nuclear and defense sectors), reliable and robust conformity assessment of production lots is imperative. While 100% inspection by a single inspector may seem like a solution for this purpose, it can be prone to human error, which can distort lot acceptance decisions. This study investigates whether a multiple-inspector sampling inspection—that is, an inspection limited to a portion of the lot but conducted by a plurality of independent inspectors—can outperform a 100% inspection by a single inspector, in these contexts. Operating-characteristic (OC) curve models were developed for both approaches, taking inspection errors into account and comparing their performance through analytical formulations and realistic examples. To simplify the analysis, this contribution focuses on sampling inspections based on single sampling plans (SSPs). Results demonstrate that incorporating multiple independent inspectors into a SSP can significantly stabilize the OC curve, maintaining lot-acceptance behaviour close to the ideal error-free scenario. Moreover, the multiple-inspector sampling strategy tends to reduce the total number of inspections needed, compared to 100% inspection, especially for moderate numbers of inspectors. In conclusion, these findingssuggest that multiple-inspectorsampling is a practical and effective way to obtain robust lot-acceptance decisions, protecting them from inspection-error distortions.