Acceptance Sampling by Attributes - Compare

Acceptance sampling can determine whether an entire lot of product should be accepted for use or rejected. With attributes, you typically inspect visually for the presence of certain characteristics, such as stains, rips, or scratches and record the number defects or the number of defective units.

With Minitab, you can:

·    Create a sampling plan – determine how many units to inspect from a lot of parts and determine how many defects/defective units are allowed.

·    Compare various sampling plans – see the effects of varying sample size and acceptance number on the plan risk.

Acceptance sampling does not improve the quality of the process in any way and is not a substitute for good quality control processes, but it is useful as a decision-making tool for accepting or rejecting products and services.

A grocery store receives a shipment of 25,000 plastic grocery bags several times a week. The receiving department has implemented a sampling plan to inspect the bags to determine whether they are acceptable for use. With a lot size of 25,000 bags, the store sets the acceptable quality level (AQL) to 2% defective and the rejectable quality level (RQL) to 5% defective. Using a producer's risk (alpha) of 0.05 and a consumer's risk of 0.10, Minitab determines that an appropriate sampling plan is to inspect 306 bags. If 10 or fewer defective bags are found, the store will accept the entire shipment. If more than 10 defective bags are found, the store will reject the entire shipment and send them back to be sorted.

The receiving department wants to compare the risks when inspecting fewer bags. You can also compare risks with accepting more defectives with this type of analysis.