Approximates the relationship between the quality of the incoming material and the number of items that need to be inspected, assuming that rejected lots will be 100% inspected and defective items will be reworked and inspected again (rectifying inspection).
The average total inspection per lot depends on the incoming quality, the probability that the lot will be accepted, and the sample and lot sizes.
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For example, your sampling plan specifies that you sample 52 rollers from a shipment of 500. If the actual % defective is 1.5%, the average total inspected per lot is 71.398 rollers. By plotting the ATI curve, the average inspection levels are evident. |
When incoming quality is very good, for example, no defects, then you inspect the specified sample size. When the incoming quality is very bad, for example, all defects, then you resort to 100% inspection. Normally the quality levels falls somewhere in between, so the average number inspected across many lots also falls in between 0% and 100% of the lot size.
You can also compare ATI curves to help choose the appropriate sampling plan.
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In this case, the shift supervisor thinks sampling 52 rollers from 500 is too much. You can develop curves for various sample sizes and acceptance numbers to illustrate the effect on the average total number of inspected items.
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Look at OC curves, AOQ curves, and ATI curves together when your corrective action for rejected lots is 100% inspection.
