Sampling Flashcards
When is acceptance sampling used? [2]
- Inspecting every item is not physically possible or too expensive; worker fatigue
- Testing would be destructive, such as testing eggs for Salmonella
When is 100% sampling feasible?
When the cost of inspecting an item is less than the cost of passing on a defective item.
When deciding whether to accept or reject a lot of raw material, describe risk.
- Rejection of acceptable lot: producers’ risk
- Acceptance of unacceptable lot: consumers’ risk
What is an operating characteristic curve?
Anoperating characteristic (OC) curveis a chart that displays the probability of acceptance versus percentage of defective items (or lots).
How is an operating characteristic curve interpreted?
If the lot quality is 0.093 fraction defective, then the probability of acceptance, Pa, is 0.05.
If the lot quality is 0.018 fraction defective, then the probability of acceptance, Pa, is 0.95.
Compare consumer risk and producer risk.
Consumer risk: the probability of accepting in error a lot that is defective (type II error: misdetection)
Producer risk: the probability that an acceptable lot is rejected in error (type I error: false alarm)
How is an operating characteristic curve constructed?
- Based on Poisson distribution.
- The larger the sample size the steeper the curve
- Decreasing the acceptance number is preferred over increasing the sample size
What does the producer’s point control?
The acceptance of lots that are at an AQL, with the goal of preventing good lots from being rejected.
What does the consumer’s point control?
The rejection of lots that are at a rejectable quality level, with the goal of preventing bad lots from being accepted.
Lots at the RQL, the consumer’s point quality level, will be […].
Rejected most of the time.
Lots at the AQL, the producer’s point quality, will be […]
Accepted most of the time.
What does a steep curve of a OC indicate?
The operating characteristics (OC) curve tells us how good our samples are and the probability of accepting defects. The steeper the curve,the better the sampling plan.
