Understanding Sampling Method and AQL in Random Product Inspection Some importers, who are new to quality control, may misunderstand that every piece of production should be inspected before shipment. It may be a wise choice for high value products or for shipments that tend to have very high quality risks or for really picky customers. For example, it is very common for Japanese customers to choose 100% full piece by piece inspection. However, sometimes 100% full inspection is just not workable because it is too costly and time-consuming, which may impair your margin and affect the shipping schedule. Moreover, without prior agreement most factories would be reluctant to receive 100% full inspection. In fact, for most shipments, a random inspection with statistically reasonable sample would be sufficient to meet your expectations. So how to determine a fair and rational sample size and also an acceptance level for such random inspection? There is where AQL standard should be introduced, which helps you determine whether to accept or reject a shipment based on the number and type of defects found in the pre-determined sample size. Acceptable Quality Level (AQL): also called Acceptable Quality Limits, is defined as the maximum percent defective that, for purpose of random sampling inspection, can be considered satisfactory as a process average. Inspection Levels: The AQL tables provide for three general inspection levels and four special inspection levels. These seven levels permit the user to balance the cost of inspection against the amount of protection required. Sampling Plans: A lot sampling plan is a statement of the sample size or sizes to be used and the associated acceptance and rejection numbers. Critical Defects: likely to result in unsafe condition or contravene mandatory regulation or reject by import customs. Major Defects: reduces the usability/function and/or sale of the product or is an obvious appearance defect. Minor Defects: doesn't reduce the usability/function of the product, but is a defect beyond the defined quality standard more or less reduces the sale of the products. Generally, the Critical/Major/Minor defects are defined as above and in practice specific circumstances and client requirements may also be taken into consideration.
There are basically two AQL tables. The first one tells you which ‘code letter’ to use based on the lot size and selected sampling plan, such as S-4, G-I, G-II, etc. (the most commonly used inspection level for consumer goods is General Inspection Level II). For example, I assume your ‘lot size’ (which means quantity) is between 3201pcs and 10,000pcs, and that your inspection level is ‘II’. Consequently, the code letter is “L”.