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INTRODUCTION -- This page will compare two strategies that vary the sample size depending on lot quality:
I prefer sequential sampling plans (2) over the switching rules (1) for the following reason.
SWITCHING RULES -- The switching rules switch back and forth between three sampling plans that have different oc curves. That is, the normal plan, the tightened plan, and and the reduced plan each has its own oc curve. For example switching from normal to reduced inspection gives you a plan with a worse consumers point. It is like switching from oc curve B to oc curve A below:
Strategically, reduced inspection is like saying:
"Quality has been good recently so lets reduce the sample size and increase our exposure to passing off-grade lots."
When an off-grade lot finally comes along the reduced
inspection plan has higher probability of accepting it -- compared to the normal plan.
Sequential sampling plans determine the sample size using only data from
the CURRENT lot. The ASN curve of a sequential
plan evaluates the effect of lot quality on the sample size.