SIST ISO 2859-4:2021 PDF

Overview

SIST ISO 2859-4:2021 - "Sampling procedures for inspection by attributes - Part 4: Procedures for assessment of declared quality levels" specifies single sampling plans for conformance testing. It is intended for formal inspections, audits and systematic tests used to assess whether an audit population (lot, process output, inventory, file, etc.) conforms to a declared quality level (DQL). The standard provides sampling plans at four levels of discriminatory ability (LQR levels 0, I, II, III) and defines the limiting quality ratio (LQR) as a reference for the risk of failing to contradict an incorrect declared quality level.

Key technical topics and requirements

• Sampling and decision procedure: Single sampling plans identified by sample size n and non‑rejection number c. Plans are selected from tabulated DQL values (0.01%–10.00%) and an LQR level (0, I, II, III).
• Risk control: For LQR levels I–III the design targets no more than 5% risk of contradicting a correct declared quality level (Type I error). The related risk of failing to contradict an incorrect declared quality level is limited to no more than 10% at the specified LQR.
• Non-rejection number (c): Typical non‑rejection numbers are c = 0 (level 0), c = 1 (level I), c = 2 (level II) and c = 3 (level III), with some exceptions for very small or large DQLs.
• Two quality models:
  • Conforming–nonconforming model (proportion p of nonconforming items).
  • Nonconformities model (average number λ of nonconformities per item).
• Operational rules: If the declared quality level is not tabulated, the next higher DQL is used to select the plan. Procedures require random sampling and include guidance on drawing samples, decision logic and disposition of nonconforming items.
• Informative annexes and tables: Includes probability curves, discriminatory ability tables and examples (Annex A and B).

Practical applications and users

SIST ISO 2859-4:2021 is suited to situations where objective evidence is needed that an entity conforms to a stated quality level. Typical targets include:

• End items, components and raw materials
• Materials in process and operations
• Supplies in storage and maintenance operations
• Data, records, administrative and accounting procedures
• Internal control procedures and audit populations

Primary users:

• Quality managers and QA/QC teams
• Auditors and compliance officers conducting reviews or regulatory inspections
• Statisticians and process engineers designing conformance tests
• Procurement and contract reviewers needing objective sampling evidence

Note: Unlike ISO 2859‑1 to -3 (acceptance sampling), Part 4 focuses on controlling Type I error for formal assessments rather than balancing bilateral acceptance risks.

Related standards

• ISO 2859 series (Parts 1–3 for acceptance sampling)
• ISO 3534‑1 / ISO 3534‑2 (statistics vocabulary)
• ISO 9000 (quality management fundamentals and vocabulary)

Keywords: SIST ISO 2859-4:2021, sampling procedures, declared quality levels, LQR, DQL, conformance testing, attributes inspection, single sampling plans, audit sampling.