ISO 4259-3:2020

Overview

ISO 4259-3:2020 - "Petroleum and related products - Precision of measurement methods and results - Part 3" defines a statistical methodology for regularly monitoring whether the precision (reproducibility) published in a standard test method remains representative of results achieved in practice. The standard uses data from proficiency testing schemes (PTS) and interlaboratory comparisons to compare the reproducibility achieved in PT rounds against the published reproducibility in the test method.

Key technical topics and requirements

• Scope: Applies to petroleum and related products that are presumed homogeneous and whose properties are stable over time and transport; data distribution should be approximately normal.
• Data prerequisites:
  • Results must be numeric and derived using a common standard test method with a published reproducibility (from ISO 4259-1 or equivalent).
  • Single result per participant per round (no repeats).
  • PT statistics should be based on at least 10 results (16 recommended) with at least 6 uniquely different values after outlier rejection.
• Statistical checks and preprocessing:
  • Outlier detection using GESD (generalized extreme studentized deviation) consistent with ISO 4259-1.
  • Normality assessed (e.g., Anderson–Darling or Shapiro–Wilk) at the 0.01 significance level.
  • PT standard deviation calculated using the root-mean-square method.
• Main test: Compare the PT round reproducibility (S_R_PT) to the published reproducibility (S_R_pub) by forming a variance ratio and performing an F‑test.
  • Published reproducibility may be adjusted by a k‑value (table provided) or, if degrees of freedom (df) are unknown, divide by 2.888 (default based on df = 30).
  • The larger variance is placed in the numerator; use the upper 97.5 percentile of the F-distribution as the critical value for a 5% two‑sided test.
  • If the variance ratio exceeds the critical F, the published reproducibility is considered inconsistent with the PT results for that round.
• Monitoring individuals: Annex B provides guidance on using z‑scores from PT rounds to track individual laboratory performance over time.

Practical applications and who uses it

• PT scheme providers: design reports and statistical evaluations aligned with ISO 4259-3 requirements.
• Testing laboratories and QA managers: verify that published method precision matches routine performance; monitor long‑term performance using z‑scores.
• Standards committees and method authors: validate and update published reproducibility values using field PT data.
• Accreditation bodies and regulators: assess ongoing method performance and conformity in interlaboratory programs.
• Industry quality teams (refining, fuels, lubricants): ensure measurement consistency across suppliers and service labs.

Related standards

• ISO 4259-1 - Determination of precision data in relation to methods of test
• ISO 13528:2015 - Statistical methods for proficiency testing by interlaboratory comparison
• ISO/IEC 17043 - General requirements for proficiency testing providers

Keywords: ISO 4259-3:2020, precision of measurement methods, proficiency testing schemes, F-test variance ratio, published reproducibility, petroleum testing, z-score monitoring, interlaboratory comparisons.