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Knowledge from the field of proficiency testing and comparative measurement

The knowledge area proficiency testing answers questions on the topics of comparative measurement, intercomparison and bilateral comparison.

What is a proficiency test or comparative measurement?

"Evaluation of the performance of a participant according to previously established criteria by comparisons between laboratories" (DIN EN ISO/IEC 17043:2010).

The performance of a measurement or test task by several (at least 2), independent laboratories. The results of the different laboratories are compared and evaluated by the provider of the test. The goal is to determine the performance of the participants under equal conditions. In this way, the laboratories are given the opportunity to prove their testing competencies or to identifysources of error as well as potential for improvement .
Testo Industrial Services does not distinguish between proficiency tests and comparison measurements; the content and scope are identical for both terms. Only proficiency tests can be performed in an accredited framework according to DIN EN ISO/IEC 17043.

Difference intercomparison/interlaboratory comparison and bilateral comparison:

Proficiency tests or comparative measurements can be carried out as interlaboratory comparisons/interlaboratorytests; several laboratories are involved in this. An additional term used in the literature is the "star-like ring comparison". In addition, we are able to perform bilateral comparisons , involving only one additional laboratory.

What is a ring comparison/ring test?

Within an interlaboratory comparison/interlaboratory comparison, a specific measurement or test task is performed by a group of laboratories independently of each other, can also be regarded as a performance test. An interlaboratory test to evaluate participant performance is called a proficiency test or comparative measurement.

What is a bilateral settlement?

In a bilateral comparison, two laboratories are compared, the pilot laboratory and the requesting laboratory. The advantage here is that, to a certain extent, the requirements of the laboratory can be met individually. In addition, the execution time is usually shorter compared to the interlaboratory comparison.

What is understood by the term pilot laboratory?

The pilot laboratory is responsible for organizing and performing the comparative measurement and for evaluating the results.


  • Many years of experience in the measurand of the calibration object
  • Accreditation for the corresponding calibration object and the procedure with the intended scope


  • Propose task description incl. metrological scope
  • Discussion and coordination with the participants
  • Formulate and prepare technical protocol with all requirements of the measurement task

Who can participate in a proficiency test or comparative measurement?

No matter if interlaboratory test, intercomparison, or star-like comparison. Any number of laboratories can participate in an interlaboratory comparison. Similarly, individual laboratories can compare themselves directly with Testo Industrial Services in a bilateral comparison. Accreditation from the participating laboratories on the content of the interlaboratory comparison is not necessary. This means that companies with calibration and testing laboratories that are not accredited can also participate.

What are the necessity and contents of proficiency tests?

The participation in Proficiency tests and comparison measurements is mandatory for accredited laboratories according to DIN EN ISO/IEC 17025. These comparison measurements represent an important element in the validation of calibration procedures and results in the quality management of a laboratory operation and provide an external method for quality assurance of the measurement procedures. 
Within the comparative measurements and proficiency tests, identical test equipment is examined by different laboratories according to the same specifications. As a provider, Testo Industrial Services compares the measurement results obtained and makes statements about the general measurement uncertainty as well as about the quality of the measurements of all participants.

What advantages do the comparative measurements offer?

Comparative measurements and proficiency testing, or internationally known as Interlaboratory Comparison (ILC), are used in the following cases: 

  • Quality assurance of laboratory tests and measurements
  • Verification of the measurement uncertainty of a measurement method
  • Comparison of calibration processes with other laboratories
  • Compliance with the requirements according to DIN EN ISO/IEC 17025:2018
  • Proof of competence towards customers, superiors and authorities

What are the tasks of a proficiency testing and comparative measurement provider?

Testo Industrial Services is the provider responsible for planning and organizing proficiency tests and comparative measurements. In addition to the coordination on time, content and technical issues, the evaluation, using statistical methods and reporting, is also carried out by the provider.