How to select a suitable proficiency testing scheme

Laboratories wishing to undertake proficiency testing can acquire information on the existence of specific PT schemes via various channels: peer laboratories, the accreditation body, or the internet database EPTIS. A large variety of PT schemes are available, and so a laboratory needs to carefully select the most appropriate scheme for their needs.

The following considerations may help laboratories to make a suitable selection:

• The PT test item should resemble the laboratory's routine samples being tested as closely as possible. Relevant characteristics include the measurand and its value, and the matrix of the material

   

• The PT should be practical, for example as regards the frequency of operation, the choice and number of PT test items, the cost of participation, the timing and location and other parameters.

   

• The PT provider should operate a management system in accordance with the relevant international guides and standards. A number of PT providers offer schemes which have been accredited.

   

• The traceability and uncertainty of the assigned value should be fit for the laboratory's purpose. Assigned values can be established in many different ways, and each of the approaches may provide different information to the participant as regards traceability and uncertainty.

   

• The purpose of the PT should be compatible with the purpose of the laboratory's measurements. As an example, if it is the aim of a PT scheme to test for compliance with national legislation it may not be suitable for a laboratory with major foreign customers.

   

• The purpose of a PT is reflected in the standard deviation for proficiency assessment, the denominator of the z-score. Laboratories have the freedom to re-evaluate their PT performance against other assessment criteria that are more fit for their purposes.