Rectifying Sampling Inspection by Variables or Attributes? Combined Inspection

Acceptance sampling, one of the techniques used in quality control, is analysed in present paper. We shall study sampling inspection plans when the remainder of a rejected lot is inspected, i.e. rectifying plans. These plans were introduced by Dodge and Romig for inspection by attributes (each inspected item is classified as either good or defective). Analogous rectifying plans for inspection by variables with one specification limit for the quality characteristic were introduced by the author of this contribution. In present article we shall consider combined inspection (all items from the sample are inspected by variables, but remainder of a rejected lot is inspected only by attributes). We shall show that the combined inspection is the best in many situations. Using plans for combined inspection we can often achieve significant savings of the inspection cost under the same protection of producer and consumer.