Overview
ISO/TR 21074:2016 provides practical guidance on applying ISO 5725 principles to determine repeatability and reproducibility of precision tests used in standardization work for the chemical analysis of steel. It explains the recommended experimental structure, data presentation, statistical evaluation (using Cochran’s and Grubbs’ tests), and calculation of precision parameters. An example using precision test data from ISO 5725‑3:1994 (Table D.2) for the precision test in ISO 9647:1989 is included.
Key topics
- Precision test structure: Recommends a 3‑factor, staggered‑nested design (e.g., two repeatability measurements on Day 1 and a time‑different measurement on Day 2) to capture repeatability and intermediate precision.
- Sample homogeneity: Emphasizes verifying sample homogeneity (especially when not using certified reference materials) before starting interlaboratory precision tests.
- Laboratory and level selection: Practical guidance on the number of participating laboratories (commonly 8–15, preferably across multiple countries) and the number of concentration levels (minimum two levels per decade).
- Data representation: Instructions for tabulation, appropriate number of decimal places, and graphical plotting for each level to visualize data distribution and laboratory performance.
- Statistical evaluation:
- Cochran’s test to detect laboratories with anomalously large within‑laboratory variance (intralaboratory repeatability).
- Grubbs’ test to detect outlying laboratory means (between‑laboratory consistency).
- Procedures for treating outliers and removing entire laboratory data sets when warranted.
- Precision calculation and smoothing: Steps to compute repeatability and reproducibility variances per ISO 5725‑3, represent results, derive functions linking level and precision parameters, and determine smoothed precision and scope.
Applications and who uses it
ISO/TR 21074 is intended for:
- Standards committees and convenors developing or updating chemical analysis methods for steel.
- Laboratory managers and analysts planning interlaboratory (collaborative) precision studies and method validation.
- Metrologists and statisticians performing statistical evaluation of precision data and advising on outlier treatment.
- Accreditation bodies and quality professionals who assess method performance, uncertainty components, and compliance with international practices.
Practical uses include designing interlaboratory trials, validating analytical methods for steel chemistry, preparing precision tables for standards, and producing defensible repeatability/reproducibility statements for technical documents.
Related standards
- ISO 5725‑1 / ‑2 / ‑3 - Methods for the determination of repeatability and reproducibility (statistical procedures and international test methods)
- ISO 9647:1989 - Example precision test used in the report
Keywords: ISO/TR 21074:2016, ISO 5725, repeatability, reproducibility, precision tests, chemical analysis of steel, Cochran’s test, Grubbs’ test, interlaboratory study, method validation.
Open preview (PDF)Application of ISO 5725 for the determination of repeatability and reproducibility of precision tests performed in standardization work for chemical analysis of steel
