This thesis develops a system of conditional sampling inspection plans which can bring a sizable saving in the amount of inspection when the process quality is relatively stable.
These plans are composed of three stages. In the first stage, the decision to accept or reject the lot is based on the information obtained from the current lot. When a decision is not made in the first stage, a second stage is introduced and the information from the immediately preceding lot as well as the information from the current lot is used for the decision. When a decision is not made in the second stage either, the decision is deferred until the information from the immediately following lot is obtained.
Existing tables for constructing double samling plans with $n_2=2n_1$ can be used to find the parameters of these plans. The response delay to the change in process quality and the deferred events may be considered as shortcomings of these plans. However, these are not serious in practical applications, and the reduction in sample size may more than offset these shortcomings.
