An acceptance sampling plan fixes a sample size n and an acceptance number c: inspect n units at random, accept the lot if c or fewer are defective, otherwise reject or screen it. Standard tables such as ANSI/ASQ Z1.4 and ISO 2859-1 index plans by lot size, inspection level and AQL, with switching rules between normal, tightened and reduced inspection. Sampling decides the fate of lots; it does nothing to improve the process that made them.
Incoming is n of 125, accept on 3 for that connector. Lot 7 had 5 rejects, so it goes back to the supplier.
Zero-acceptance plans, c of 0, are popular because any defect rejects the lot, but at the same sample size they also reject more good lots.
Also heard as
- lot acceptance sampling
- sampling plan
- LASP
Related terms
AQL
Acceptable quality level: the defect rate a sampling plan is built to pass most of the time, the good end of its OC curve.
LTPD
Lot tolerance percent defective: the poor quality level that a sampling plan should reject with high probability.
Operating characteristic curve
Graph of a sampling plan's probability of accepting a lot against the lot's true defect rate.
Sort
Either the wafer-level electrical test that bins every die, or a 100 percent inspection that screens suspect parts.