ISO 5725-6:1994

Overview

ISO 5725-6:1994 - “Accuracy (trueness and precision) of measurement methods and results - Part 6: Use in practice of accuracy values” explains how to apply accuracy data (trueness and precision) in routine metrology and laboratory practice. The standard assumes that estimates of precision and bias have been obtained according to the ISO 5725 series and focuses on practical procedures for using those accuracy values to judge test results, monitor stability, assess laboratory performance and compare alternative measurement methods. It applies to measurement methods that produce a single numerical result on a continuous scale.

Keywords: ISO 5725-6, accuracy, trueness, precision, repeatability, reproducibility, measurement methods, metrology, laboratory assessment.

Key topics

• Repeatability and reproducibility limits - defines practical limits (e.g., r and R) used when comparing test results. The standard uses a rounded critical factor (2.8) for 95% critical differences (r = 2.8·σr, R = 2.8·σR).
• Critical difference calculations - shows how to compute critical differences for:
  • two single results,
  • means from groups of different sample sizes (using the combined standard deviation),
  • comparisons with reference values and grand means.
• Acceptability checks and decision rules - procedures for identifying suspect or aberrant results and guidance on handling and reporting them (including when to investigate or discard data).
• Stability (quality control) within a laboratory - methods to assess temporal stability of results and to implement ongoing internal quality control.
• Laboratory assessment and competency - use of repeatability/reproducibility standard deviations to evaluate whether a laboratory can satisfactorily use a standard measurement method.
• Comparison of alternative measurement methods - recommended approaches to compare candidate methods, including experiments for accuracy and routine method validation.

Applications

• Routine quality control and acceptance testing where measurement variability must be interpreted.
• Inter-laboratory comparisons, proficiency testing and certification schemes to flag unacceptable differences.
• Method validation and standardization projects comparing a candidate method with a reference method.
• Regulatory and contractual situations where decisions depend on whether differences exceed statistically justified limits.
• Designing control charts and stability monitoring based on established precision values.

Who should use this standard

• Laboratory managers and quality assurance personnel
• Metrologists and test method developers
• Accreditation bodies, regulators and auditors
• Statisticians involved in measurement uncertainty and method comparison
• Proficiency testing providers

Related standards

• ISO 5725-1 to ISO 5725-5 (accuracy, precision and trueness methods)
• ISO 8258 (Shewhart control charts)
• ISO Guide 33 / ISO Guide 35 (reference materials)
• ISO/IEC Guide 25 (competence of calibration & testing laboratories)

ISO 5725-6 provides practical, statistically founded decision rules for interpreting measurement differences and maintaining reliable measurement performance in labs and testing programs.