Operating characteristic curve
The operating characteristic curve for a sampling plan quantifies the risks. The OC curve for an attribute plan is a graph of the percentage defective in a lot versus the probability that the sampling plan will accept a lot. The figure describes the OC curve:
Figure : OC curve
The figure explains that the acceptance level at A has about 98% chance of being accepted. B has 50% of defective and has 23 % chance of being accepted, C has about 30% defective and has 3% chance of being accepted.
The OC curve can be developed by determining the probability of acceptance for many values of incoming quality. The probability of acceptance is the probability that the number of defectives in the sample is equal to or less than the acceptance number for the sampling plan.
The OC curve for a particular plan states only the chance that a lot having certain defective percentage would be accepted by the sampling plan.
The confidence level in connection with a particular defective percentage might not be stated by OC curve, the final quality achieved post completion of inspections might not be predicted exactly by the OC curve.