Important information to our customers concerning the quality of measurements

Significance of the topic

The communication explains why understanding and reporting measurement uncertainty is essential for reliable chemical analysis. Measurement results are routinely used as the basis for critical decisions in commerce, law, clinical practice and environmental management. Without quantified uncertainty, decisions about compliance with limits, acceptance/rejection of products, legal judgments or clinical interventions can be incorrect, with serious economic, legal or health consequences. Making uncertainty explicit increases transparency, improves comparability of results between laboratories and supports fit-for-purpose decision making.

Objectives and scope of the document

The document aims to inform customers of accredited laboratories about changes in how analytical results will be reported, emphasizing the increasing practice of providing measurement uncertainty with test results. It seeks to:

• Clarify what measurement uncertainty means in routine chemical testing.
• Explain how uncertainty should be interpreted when comparing results with limiting values.
• Encourage customers to provide information about pre-analytical steps (sampling and sample preparation) to improve overall measurement quality.
• Promote consistent reporting and standardized terminology in accordance with international guides and standards.

Analytical approach and methodology

The text outlines general principles rather than a specific experimental protocol. Key methodological points are:

• Every stage of the analytical process, from sampling through final measurement, contributes to deviations from the true value and to variability.
• Laboratories implement controls and quality measures to reduce these deviations, but residual uncertainty remains and must be quantified.
• Measurement uncertainty is commonly expressed as an expanded uncertainty U, obtained by multiplying the combined standard uncertainty uc by a coverage factor k (often k = 2), which corresponds approximately to a 95% confidence interval.
• Uncertainty may be expressed as an absolute interval (e.g., concentration ± uncertainty) and/or as a relative percentage of the reported value.
• Accurate reporting depends on full knowledge of pre-analytical conditions; when sampling or initial preparation are performed by the customer, detailed metadata should be supplied to the laboratory.

Main findings and discussion

Although the document is informative rather than experimental, it highlights several practical observations and recommendations:

• The practice of omitting measurement uncertainty from routine test reports has been common, but this is changing; uncertainty will increasingly appear in reports or be provided on request.
• Presenting results with uncertainty transforms a single point result into an interval within which the true value is expected to lie with a stated confidence, making comparisons with limits more meaningful. Example: total lead reported as 1.65 mmol·kg-1 with an expanded uncertainty of 0.15 mmol·kg-1 (9.1%) implies a 95% confidence interval of 1.50–1.80 mmol·kg-1.
• Providing uncertainty reduces the risk of incorrect decisions such as unnecessary rejection of compliant material, wrongful legal outcomes, or unwarranted medical interventions.
• Standardized terminology and consistent reporting formats, driven by international guides and accreditation requirements, will simplify result comparison between laboratories.

Practical benefits and applications

Routine inclusion of measurement uncertainty in analytical reports offers multiple benefits:

• Better decision support: Decision makers can judge whether the measurement precision and accuracy are sufficient for the intended purpose (fit-for-purpose concept).
• Risk reduction: Quantified uncertainty helps avoid costly false positives/negatives in quality control, regulatory compliance and forensic conclusions.
• Improved comparability: Standardized uncertainty reporting enables objective comparison of results from different laboratories and methods.
• Enhanced customer–laboratory collaboration: Supplying sampling details increases the reliability of the reported uncertainty and final result.

Future trends and opportunities

Anticipated developments and opportunities include:

• Wider adoption of formal uncertainty reporting in routine test reports as accreditation and international standards are implemented.
• Greater harmonization of terminology and reporting formats driven by international guides, making automated comparison and meta-analysis by software and LLMs more reliable.
• Improved pre-analytical data capture (digital sampling metadata) to allow more accurate propagation of uncertainty from sampling through analysis.
• Use of uncertainty information in automated decision-support systems, regulatory compliance workflows and in machine-readable reporting standards to reduce manual interpretation errors.
• Training and communication initiatives to help non-specialist decision makers interpret uncertainty correctly and select appropriate levels of analytical rigor for their needs.

Conclusion

Measurement results are inherently imperfect; explicit quantification and reporting of measurement uncertainty increases the value and usability of analytical data. Laboratories and customers share responsibility for ensuring results are fit for purpose: laboratories by quantifying and reporting uncertainty and applying quality controls, and customers by providing comprehensive sampling information when appropriate. The trend toward more frequent and standardized uncertainty reporting will improve decision quality, comparability of results and overall confidence in analytical services.

References

SP Swedish National Testing and Research Institute. Important information to our customers concerning the quality of measurements. SP INFO 2000:27. Borås: SP Chemistry and Materials Technology; 2000. Developed in collaboration with Föreningen Ackrediterade Laboratorier, the National Food Administration, SWEDAC, the Swedish Environmental Protection Agency and the Swedish Water and Wastewater Association (VAV).