What is Proficiency Testing?
Proficiency testing determines the performance of individual laboratories for specific tests or measurements and is used to monitor laboratories’ continuing performance.
Proficiency testing is also called interlaboratory comparison. As this term implies, proficiency testing compares the measuring results obtained by different laboratories.
In a proficiency test one or more artifacts are sent around between a number of participating laboratories. Each laboratory measures the artifacts (e.g. a ring gage or a set of gage blocks) according to a given set of instructions and reports its results to the administrator.
The results reported by each laboratory for a measurand are compared to the reference value for that measurand. The reference value can be determined in various ways. The two most common ways are to use a reference laboratory or use the average of the values reported by the participants.
HN Proficiency Testing uses reference laboratories to provide the reference values. The reference laboratories are chosen for each measurand by the technical advisor for the proficiency test in question based on his or her knowledge of the laboratory and the uncertainty the laboratory is able to quote for the measurand.
The reference laboratories are generally A2LA accredited laboratories (accredited for the measurand in question), which have been assessed by the technical advisor.
HN Proficiency Testing purchases an accredited test or calibration from the reference laboratory on a commercial basis to establish the reference value for a proficiency test. We are therefore able to select what we consider the most competent laboratory to provide the reference value for each test.
There are different ways to evaluate the results of a proficiency test. For the type of proficiency tests offered by HN Proficiency Testing, the result reported by a participating laboratory for a measurand is compared to the reference value by calculating the En-value.
The En-value is calculated as follows:
VLab is the value reported by the participating laboratory
VRef is the reference value
ULab is the uncertainty reported by the participating laboratory
URef is the uncertainty of the reference value
The uncertainties shall be expressed using k=2, which corresponds to a 95 % coverage.
The result is considered successful, if the result of the proficiency test is -1 ≤ En ≤ 1. In this case the participating laboratory agrees with the reference value within the stated uncertainty of the two. Based on a number of assumptions, this is expected to be the case at least 95 % of the time.
If a laboratory has any unsuccessful results, i.e En < -1 or En > 1, it is expected that the laboratory investigates the reason for the disagreement and implements corrective action.