Chain-Deferred Inspection Plans

Abstract

SUMMARY The paper proposes plans that improve on existing chain and deferred sampling plans. The plans are mixed in the sense that they combine elements from both chained and deferred plans. This combination gives an operating characteristic curve closer to that of the traditional double sampling plan than either the simple chain or the simple deferred inspection plan when there is a trend in process quality. The plans require fewer items to be sampled than the traditional double sampling plans and have a delay in the decision only where there are indications that quality is poor. The relative ease with which these plans can be made compatible with the double sampling plans in the MIL‐STD‐105D and some other similar schemes is noted.

A Modified ChSP-1 Chain Sampling Plan, MChSP-1, with very Small Sample Sizes

“…In general, if there is a trend in process quality, the chain and deferred plans decide in a reverse way on a lot of a given quality as given below (see Osanaiye (1983) Osanaiye (1983) therefore suggested to adopt a strategy of chain-deferred inspection to ensure protection against quality trends. Let i be an even number and the procedure of the MChSP-1 plan is modified as a chain-deferred plan such that one utilizes the results of f preceding and f succeeding lots.…”

Conditional Zero Acceptance Number (COZAN) Plan

“…The utility of the COZAN plan can be felt differently from the existing conditional sampling plans [1,[5][6][7][8][9][10][11][12]. These conditional plans were not developed with the aim of reducing the sample size of an Ac = 0 plan.…”