ITPEC FE Morning April 2021 Question 77
In a sampling inspection, which of the following can be used to ascertain the probability of acceptance of a lot with a certain defective ratio?
Explanation
OC curve — plots the probability of accepting a lot against the lot's defective ratio.
The OC (operating characteristic) curve of a sampling plan, set by the sample size and the acceptance number, shows for each defective ratio how likely the lot is to pass. Good lots should be accepted with high probability and bad lots rejected; the curve shows the producer's risk and the consumer's risk of the plan.
Answer (d)
Why not others:
- •(a) Bathtub curve — the failure rate of equipment over time: early failures, random failures, wear-out failures
- •(b) Gompertz curve — an S-shaped growth curve, used for example to predict the cumulative number of bugs found during testing
- •(c) Logistic curve — another S-shaped growth curve, used for demand growth and the spread of new products
Key rule: Acceptance probability against defective ratio is the OC curve; failure rate against time is the bathtub curve; S-shaped cumulative growth is Gompertz or logistic.
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