Acceptance Sampling is used to make dispositions on accepting or rejecting a lot (or batch) of manufactured products. It is most often used to evaluate products that are received from vendors or suppliers. Acceptance Sampling is a cost effective solution that should be considered when:
- Destructive testing is required to assess product quality
- 100% inspection isn't feasible due to the cost or time involved
- A supplier has a strong history of supplying acceptable products
Attribute sampling plans provide lot accept/reject decisions based on the number of defects or defectives found in a shipment. C=0 plans are included as well as plans based on acceptable quality levels where a certain number of defects/defectives are allowed before the lot is rejected.
Variable sampling plans rely on actual measurements to make accept/reject decisions. Variable sampling plans typically require significantly fewer samples than attribute plans and are therefore regarded as more cost effective and efficient.
ProFicient variables sampling plans are based on four input parameters: Acceptable Quality Levels, Lot Tolerance Percent Defective, Producer’s Risk and Consumer’s Risk.
Acceptable Quality Level (AQL)
The Acceptable Quality Level (AQL) is generally defined as the percent defectives that the plan will accept 95% of the time. Lots that are at or better than the AQL will be accepted 95% of the time. If the lot fails, one can say with 95% confidence that the lot quality level is worse than the AQL. Likewise, it can be said that a lot at the AQL that is acceptable has a 5% chance of being rejected. The AQL isn’t necessarily the quality level that is being produced or the quality level that is being accepted. It may not even be the quality goal. It is simply the percent defective at the Producer’s Risk (Alpha) or the probability of rejecting the acceptable.
Lot Tolerance Percent Defective (LTPD)
The Lot Tolerance Percent Defective (LTPD) is generally defined as percent defective that the plan will reject 90% of the time. We can say that a lot at or worse than the LTPD will be rejected 90% of the time. If the lot passes, we can say with 90% confidence that the lot quality is better than the LTPD. We could also say that a lot at the LTPD that is defective has a 10% chance of being accepted. The LTPD is the percent defective at the Consumer’s Risk (Beta) or the probability of accepting a defective sample. The Consumer’s Risk is typically 10%.
Learn more about Acceptance Sampling
To learn more about Acceptance Sampling, view the recording of our Lot Acceptance Sampling webinar.