Overview
ISO 2859-3:2005 - "Sampling procedures for inspection by attributes - Part 3: Skip‑lot sampling procedures" specifies generic skip‑lot sampling methods for acceptance inspection by attributes. The standard provides rules to reduce inspection effort for suppliers with documented, effective quality assurance and stable product quality. Reduction is achieved by the random selection of lots (with specified inspection frequencies) so some lots are accepted without inspection. It applies to end items, sub‑assemblies, components, raw materials and materials in process.
Key topics and technical requirements
- Skip‑lot principle: Extends random sampling of items (ISO 2859‑1) to the random selection of lots for possible omission from inspection.
- Inspection frequencies: Defined probabilities that a lot will be inspected (typical frequencies: 1/2, 1/3, 1/4, 1/5).
- Supplier qualification: Requirements for documented quality systems, in‑house inspection, and capability to detect quality shifts before skip‑lot is permitted.
- Product qualification: Assessment of product stability and prior quality history; a qualification score is used to decide qualification, frequency changes, interruptions, disqualification and requalification.
- Sampling and lot selection: Procedures for selecting which lots are inspected under different states (qualification, skip‑lot, interruption) and how to apply attribute sampling plans.
- Interruption, disqualification and requalification: Rules for ceasing skip‑lot privileges, returning to lot‑by‑lot inspection, and conditions for resuming reduced inspection.
- Roles and responsibilities: Duties of the supplier, inspection agency (independent third party) and the responsible authority in implementing, assessing and managing skip‑lot inspection.
- Compatibility and limitations: Guidance on when to use skip‑lot vs. reduced inspection and compatibility with ISO 2859‑1; limitations for isolated lots and non‑continuing series.
Practical applications
- Reduce inspection costs and time for high‑quality, stable production where supplier controls are proven.
- Apply to acceptance inspection of finished products, components, raw materials and in‑process materials in manufacturing, assembly and supply chains.
- Useful in quality assurance programs where incoming inspection resources are limited and supplier performance data justify lower inspection effort.
Who should use this standard
- Quality managers, purchasing professionals and inspection agencies implementing acceptance sampling.
- Suppliers seeking to qualify for skip‑lot programs and purchasers or third‑party inspectors managing inspection frequency agreements.
- Statisticians and process engineers assessing sampling strategies for attribute inspection.
Related standards
Keywords: ISO 2859‑3:2005, skip‑lot sampling, sampling procedures, acceptance inspection by attributes, inspection frequency, supplier qualification, qualification score, lot selection.