1. What is a sampling plan? A sampling plan allows an auditor or a researcher to study a group (e.g. a batch of products, a segment of the population) by observing only a part of that group, and to reach conclusions with a pre-defined level of certainty. In this article I cover these cases in depth (hit the links below to skip to the relevant section): The buyer wants to follow the most common plan to inspect a supplier's batch of products The manufacturer implements a continuous … [Read more...]
What is the “AQL” (Acceptance Quality Limit) in simple terms?
What Does AQL Mean? 'AQL' stands for 'Acceptance Quality Limit', and is defined as the "quality level that is the worst tolerable" in ISO 2859-1. It represents the maximum number of defective units, beyond which a batch is rejected. Importers usually set different AQLs for critical, major, and minor defects. Most Asian exporters are familiar with this type of setting. For example: "AQL is 1.5%" means "I want no more than 1.5% defective items in the whole order quantity, on average over … [Read more...]
The Special Inspection Levels in the AQL Tables
A few years ago I wrote about the inspection levels, but some people are still confused about the "special" levels (S1, S2, S3, and S4). Here is what the ISO 2859-1 standard says (emphasis mine): The inspection level designates the relative amount of inspection. Three inspection levels, I, II and III, are given in Table 1 for general use. Unless otherwise specified, level II shall be used. Level I may be used when less discrimination is needed or level III when greater discrimination is … [Read more...]