Sequential tests to monitor lot attribute quality in the presence of inspection errors

Recent studies show that errors in inspection cannot be ignored when one uses control charts, or the single, double, or multiple sampling plans. This paper investigates the effect of Type I (rejecting a good item) and Type II (accepting a defective item) inspection errors on Wald’s SPRT applied to lot attribute quality tests. OC, ASN functions, and the sensitivity of the SPRT to error levels are studied and an asymmetry in sensitivity to Type I/Type II errors is shown. The paper generalizes the Kroeber nomogram to reduce the effort in the design of sequential sampling plans when inspection is error prone.