Optimal designing of multiple deferred (dependent) state repetitive group sampling plan for variables inspection

In this paper, we propose the designing methodology of multiple deferred (dependent) state repetitive group sampling plan for lot sentencing when the quality characteristic of the product follows normal distribution. This sampling plan incorporates the features of two existing sampling plans such as multiple deferred (dependent) state sampling plan and repetitive group sampling plan. Under the proposed sampling plan, the current lot is immediately accepted if it has good quality and rejected if the lot quality is poor. But, the decision on the current lot depends on the decision of the successive/preceding lots and/or additional samples from the current lot when the current lot is of moderate quality. Two-points on the operating characteristic curve approach is used to determine the optimal plan parameters for various combinations of acceptable quality level and limiting quality level. In determination of plan parameters, two cases are considered such as standard deviation is known and unknown. An application of the proposed sampling plan in industries is discussed with real life example. The significance of the proposed plan is explained by a comparative study.