1.1 While there are a number of uses for interlaboratory tests, and variations in their design and implementation, it is still possible to specify the essential principles that need to be considered when organizing such tests. Part A of this guide defines those principles and describes the factors that should be taken into account in the organization and conduct of proficiency testing programs.

1.2 This guide also covers how laboratory accrediting bodies, which assess technical competence of testing laboratories, should select and use proficiency testing programs (refer to Part B).

1.3 Part A of the guide is intended for use by various parties, such as accrediting bodies, regulatory authorities and clients of laboratory services which have a need to assess the technical competence of laboratories. It is also useful for laboratories in self-evaluation, but recognizes that proficiency testing is only one mechanism that can contribute to establishing equivalent confidence among users of different testing laboratories.

1.4 It is currently a condition of some accreditation bodies that laboratories participate regularly in "approved" proficiency testing programs. Therefore, it is essential that program operators comply with principles for conduct of professionally managed proficiency programs, both in terms of technical requirements and quality management (see Annexes A1 and A2).

1.5 The methods of operation within different proficiency testing organizations are not expected to be identical and this guide does not give specific operational details for interlaboratory test comparisons. It does, however, cover both measurement comparison and testing programs in which large numbers of laboratories (over 20) or small groups of laboratories (1 to 20) are tested. Therefore, the contents of this guide are intended only as a framework to be modified appropriately for particular situations.

1.6 A list of some relevant references is given in Appendix X1.