Statistical Sampling Statistical Sampling is widely used to decide whether or not to accept or reject a production lot without checking every single items of the lot. It is equally applicable to incoming inspections of shipments of raw materials or partially finished products, products at various stages of manufacture, and finished products as well as outgoing shipments.
MIL-STD-105E / ISO2859-1 / ANSI/ASQC Z1.4 It is a random sampling plan that indicates the number of units of product from each lot or batch to be inspected (sample size or series of sample sizes) and the criteria for determining the acceptability of the lot or batch (acceptance and rejection numbers), which comprises of Sample Size Code Letter and Acceptable Quality Level (AQL).
Acceptable Quality Level (AQL) The AQL is the maximum allowed percent defective. The designated value of defects, expressed as a percentage by the particular sampling procedure and level used will identify what the buyer will normally accept in the majority of cases.
Defect Classification Defects detected during visual inspection are classified within 3 categories, "Critical", "Major" and "Minor" and the normal definitions are: Critical Defect: A defect that fails to meet mandatory regulations and/or affects the safety of the consumer when using the product. Major Defect: A defect that is likely to result in product failure, reduction the usability of the product and obvious appearance defect affecting the salability of the product. Minor Defect: A defect that is not likely to reduce the usability of the product, but is likely to reduce the salability or a discrepancy from the defined quality standard.