An operating characteristic curve puts probability of acceptance on the vertical axis and incoming percent defective on the horizontal. A perfect plan would be a vertical step, accepting every good lot and rejecting every bad one; real plans give an S-shaped curve that steepens as the sample size grows. The AQL and LTPD are read off the curve near 95 and 10 percent acceptance, and comparing curves is the cleanest way to compare plans.
Plot the OC curve before you sign that plan. At n of 20, accept on 1, a lot that's 5 percent bad still passes 74 percent of the time.
Also heard as
- OC curve
- acceptance curve
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.
Acceptance sampling
Accepting or rejecting a whole lot based on inspecting a random sample from it against a predefined plan.
Power
Probability that a test will detect a real effect of a given size, set by sample size, noise and alpha.