Overview
ISO 28597:2017, "Acceptance sampling procedures by attributes - Specified quality levels in nonconforming items per million", defines methods for estimating and verifying very-high-quality production expressed as nonconforming items per million. It covers single-lot quality estimates and, when the production is in statistical control, process-level estimates based on multiple samples. The standard also gives guidance for selecting acceptance sampling plans (lot-by-lot) indexed by a limiting quality level (LQL) and for presuming a process quality level when prior data are inadequate.
Key topics and requirements
- Quality metrics: Expresses quality as nonconforming items per million (np/m) to improve clarity when defects are rare.
- Estimation procedures: Methods for estimating the quality of a single entity (lot) and for pooled/process estimates from several samples.
- Sampling plan selection: Use estimated or presumed process quality level to choose a sampling plan that verifies the lot does not exceed a stated LQL.
- Statistical control prerequisites: Process-level estimation applies when the process is in statistical control and cumulative inspected items (audit + lot acceptance) are adequate (recommendation: 400 or more).
- Risk indexing: Defines producer’s and consumer’s risk quality levels in np/m (e.g., producer’s risk corresponds to ~5% lot rejection; consumer’s risk corresponds to ~10% lot acceptance).
- Lot acceptance procedures: Single sampling plans indexed by LQL, with guidance on acceptance numbers, sample sizes and use of tabulated plans (Table 1 in the standard).
- Reporting and data handling: Formats for reporting estimated quality levels, data accumulation periods, and allowed data exclusion options (Annex A).
- Normative references: Links to ISO 2859‑1 and ISO 3534 series for terms and sampling scheme context.
Practical applications and users
ISO 28597:2017 is intended for organizations and professionals who need to verify extremely low defect levels and optimize inspection effort:
- Quality engineers and QA managers selecting attribute sampling plans for high-reliability products.
- Suppliers and purchasers establishing lot acceptance criteria tied to limiting quality levels (LQL).
- Auditors and conformity assessors who report quality in nonconforming items per million.
- Industries with low-defect targets (electronics, aerospace, medical devices, precision manufacturing, high-volume consumer goods).
Benefits include clearer communication of rare-defect performance, incentives for suppliers to improve quality (smaller samples for better quality), and consistent lot-by-lot verification against specified np/m targets.
Related standards
- ISO 2859-1 - Sampling procedures for inspection by attributes (AQL schemes)
- ISO 3534-1 / ISO 3534-2 - Statistical vocabulary and symbols
- ISO 28590–28599 series - Related sampling and acceptance standards (renumbered series that includes this document)
Keywords: ISO 28597:2017, acceptance sampling, attributes, nonconforming items per million, sampling plan, limiting quality level (LQL), process quality level, lot acceptance, statistical control.
