Interlaboratory Comparison (ILC)
Compare Measurement Results, Gain Deeper Insight into Your Technical Performance
Every analysis and measurement performed in a laboratory can form the basis for a reliable decision. However, evaluating the reliability of a measurement result is not limited to reviewing the laboratory’s internal quality control processes. Comparing results with data obtained from different laboratories can provide a broader perspective for assessing the performance of measurement processes.
Interlaboratory Comparison (ILC) is an important quality assessment activity based on the comparison of measurement or analytical results obtained by different laboratories using test items with the same or similar characteristics, in accordance with a predefined approach.
PT Nexus – Connecting Laboratories. Advancing Quality. aims to provide modern ILC programs that enable laboratories to objectively evaluate their technical performance based on data, assess the comparability of measurement results, and contribute to continuous improvement activities.
What Is Interlaboratory Comparison?
Interlaboratory Comparison (ILC) is the evaluation of measurement or analytical results obtained by two or more laboratories using the same or similar test items, in accordance with a defined technical and statistical approach.
These studies can help different laboratories objectively assess:
- Measurement results,
- Analytical performance,
- Methods used,
- Technical practices,
- Differences within measurement processes.
The primary purpose of ILC is not simply to rank laboratories against one another.
Its main purpose is to generate information that can contribute to understanding differences between measurement results, evaluating technical performance, and improving laboratories’ own quality processes.
Why Is Interlaboratory Comparison Important?
While achieving successful results within a laboratory is important, the comparability of measurement results with those obtained by other laboratories is also valuable from a quality perspective. ILC studies can therefore provide laboratories with a broader perspective on their performance.
Through Interlaboratory Comparison, laboratories can:
- Evaluate the consistency of measurement results,
- Compare results obtained by different laboratories,
- Investigate potential systematic differences,
- Review the performance of analytical methods,
- Investigate potential deviations within measurement processes,
- Obtain additional information regarding technical competence,
- Contribute to the improvement of quality management systems.
In this respect, ILC is an important tool that helps laboratories evaluate their own performance within a broader set of comparative data.
How Is an Interlaboratory Comparison Conducted?
The technical scope, testing area, and objectives of each ILC program may differ. However, the overall process generally consists of several key stages.
1. Defining the Program Scope
At the initial stage, the purpose of the comparison, testing or measurement area, test item, participant profile, and evaluation approach are defined. The technical design of the program is established by taking into account the characteristics of the measurement or analysis to be performed.
2. Preparation of the Test Item
It is important that the material used in the comparison study is suitable for the objectives of the program.
The preparation of the test item, assessment of its suitability, and, where applicable, evaluation of characteristics such as homogeneity and stability are important elements in supporting the reliability of the program.
3. Laboratories Perform Their Analyses
Participating laboratories perform measurements or analyses on the test items provided to them, using their routine working conditions and relevant analytical procedures.
This stage is important for assessing the laboratories’ performance under conditions that reflect their actual technical practices.
4. Collection of Results
Results obtained from participating laboratories are submitted within the defined timeframe.
As part of the PT Nexus digital process approach, the management of results and relevant documentation through the PT Nexus Online platform is intended to support a more organized and traceable process.
5. Technical and Statistical Evaluation of Data
Results obtained from participating laboratories are evaluated according to the technical and statistical approach defined for the program.
The distribution of results, observed differences, and indicators related to laboratory performance are examined to establish a meaningful evaluation.
6. Reporting of Results
At the conclusion of the program, the collected data are evaluated and a reporting process is carried out to help participating laboratories review their individual performance.
Reporting is not limited to presenting results; it is intended to provide a feedback mechanism that supports laboratories in evaluating the information obtained within their own quality management systems.
What Does ILC Bring to a Laboratory?
Interlaboratory Comparison can help laboratories evaluate their own measurement and analytical performance from an external comparative perspective.
As a result of these studies, laboratories can:
Understand Their Performance
Compare their own measurement or analytical results with those of other participating laboratories.
Identify Differences
Obtain data that can be used to investigate differences observed between results.
Review Technical Processes
Reassess analytical methods, equipment, sample preparation, and measurement processes.
Identify Areas for Improvement
Gain insight into areas where performance may need to be improved.
Support Quality Management
Use ILC results as a source of feedback within their quality management systems.
Comparability of Measurement Results
The comparability of laboratory results is as important as their reliability.
When significant differences are observed between the results of the same or similar analyses performed by different laboratories, factors such as the analytical method, equipment, sample preparation, measurement conditions, or other technical variables may need to be investigated.
Interlaboratory Comparison studies can help make these differences visible and enable laboratories to evaluate their own processes in greater detail.
For this reason, ILC is not simply a process for comparing results; it is also an evaluation approach that contributes to a better understanding of the measurement system.
ILC and Technical Competence
The technical competence of a laboratory is not determined solely by the characteristics of its equipment or the analytical methods it uses.
The ability to produce reliable results requires the combined consideration of multiple factors, including:
personnel competence + appropriate method + correct implementation + equipment performance + measurement conditions + quality control + continuous performance monitoring
ILC programs can contribute to enabling laboratories to assess the performance resulting from these factors through external comparative data.
Interlaboratory Comparison and Continuous Improvement
The data obtained from an ILC study are valuable not only for understanding the laboratory’s current performance but also for establishing future quality objectives.
When an unexpected result or difference is identified, a laboratory may review:
- Analytical methods,
- Measurement equipment,
- Calibration processes,
- Sample preparation practices,
- Personnel competence,
- Quality control records,
- Measurement conditions.
In this way, an ILC study can become part of an ongoing quality improvement cycle:
Compare → Investigate → Identify the Cause → Improve → Reassess
This approach supports laboratories in transforming comparative data into actionable insights and using them as part of their continuous improvement processes.