Analysis of a Cumulative Results Sampling Plan for Use with Sampling Tables using Zero Acceptance Numbers

The Western Electric Company has proposed a Cumulative Results Sampling Plan to supplement plans using zero acceptance numbers. The proposed plan makes use of the cumulative results of a number of previous inspection lots to determine the disposition of a subsequent lot when a sampling plan with zero acceptance number is used and only one (1) defect is found in the sample. The proposed plan has the effect of decreasing the producer's risk in the area of relatively good quality while increasing the consumer's risk only slightly at Pa (.50) over that obtained by the MIL-STD plan with zero acceptance number. At Pa (.1) the CC curve for the plan practically coincides with the corresponding MIL-STD plan with zero acceptance number. The use of the proposed plan should overcome much of the reluctance of suppliers to the application of statistical sampling to product that is submitted in small lots and may, in some instances, permit the use of sampling when 100% inspection was heretofore necessary. It is recommended that consideration be given to the general use of Cumulative Results Sampling Plans where the continued use of sampling plans with zero acceptance numbers becomes necessary.