ISO 5725-3:2023

Overview

ISO 5725-3:2023 - "Accuracy (trueness and precision) of measurement methods and results - Part 3" provides guidance on intermediate precision and alternative experimental designs for collaborative studies. The standard explains how to determine and interpret measures of precision (repeatability, reproducibility and selected intermediate precision measures), reviews when alternative designs are necessary or beneficial, and includes worked examples with specific layouts and computations. It helps laboratories and method developers characterise method variability under practical, between‑run and between‑operator conditions.

Key topics and requirements

• Scope of precision: Definitions and interpretation of trueness, precision, repeatability, reproducibility and intermediate precision in the context of standard measurement methods.
• Factor selection and modelling: Guidance on identifying relevant factors (laboratory, operator, equipment, reagent batch, time, environment, etc.), selection of factor levels, and treatment of random vs fixed effects.
• Alternative experimental designs: Practical layouts and analysis for:
  • Balanced fully‑nested, staggered‑nested and partially‑nested designs
  • Orthogonal array designs
  • Split‑level designs to avoid distorted repeatability estimates
  • Designs for heterogeneous material
  • Designs across levels
• Statistical analysis methods: Analysis of variance (ANOVA) approaches and Restricted Maximum Likelihood (REML) options are referenced (annexes include worked ANOVA/REML examples).
• Reliability and optimisation: Methods to assess the reliability of precision and overall mean estimates, reduce required participant numbers, estimate operator variability, and improve sample mean estimation.
• Worked examples: Annexes provide step‑by‑step analyses and example computations to apply the designs and interpret results.

Practical applications and users

ISO 5725-3:2023 is intended for:

• Analytical and testing laboratories validating or verifying measurement methods
• Method developers preparing single‑laboratory validation and planning collaborative studies
• Accreditation bodies and conformity assessment organizations assessing method performance
• Standards committees and statisticians designing interlaboratory studies

Typical uses:

• Estimating how much variability is introduced by operators, equipment or days (intermediate precision)
• Selecting efficient collaborative study designs that reduce workload while maintaining reliable precision estimates
• Designing experiments for heterogeneous test materials or multi‑level measurement systems

Related standards

• ISO 5725-1 - Concepts and general principles for accuracy (trueness and precision)
• ISO 5725-2 - Basic method for the determination of repeatability and reproducibility
• ISO 5725-5 - Previously addressed designs for heterogeneous materials (related content now included)

Keywords: ISO 5725-3:2023, intermediate precision, collaborative studies, reproducibility, repeatability, measurement methods, split-level design, orthogonal array, heterogeneous material, ANOVA, REML.