Why does IFS Cloud reject a lot through acceptance sampling (AQL 0.25, inspection level II, sample of 3) when every measured value in the shop order test operation is inside the spec limits?
Technical details
Shop order test operation with acceptance sampling: AQL 0.25, inspection level II, sample size 3. All readings within spec limits, but the acceptance sampling status is Rejected. The AQL applies to the share of nonconforming items across the whole lot; a high standard deviation in the readings leads IFS to estimate that more than 0.25% of uninspected items fall outside spec.
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✓ Accepted answer
This is expected behaviour. The AQL is the acceptable share of nonconforming items across the whole lot, not just the sample. With a high spread (standard deviation) in the readings, IFS estimates that more than 0.25% of uninspected items would fall outside spec, so it rejects the lot. Tighter, more consistent readings or a different AQL change the outcome. Caveat: a follow-up about swapping the ISO-based standards for a zero-acceptance plan was not answered in the thread.
Prerequisites and limitations
A follow-up about replacing the ISO-based standards with a zero-acceptance plan was not answered in the thread. Release not stated beyond IFS Cloud.