While there are a number of uses of interlaboratory comparisons, and variations in their design and implementation, it is still possible to specify the essential principles that need to be considered when organizing such comparisons. This part of lSO/IEC Guide 43 de-fines those principles and describes the factors which should be taken into account in the organization and conduct of proficiency testing schemes.

Part 2 of lSO/IEC Guide 43 describes how laboratory accreditation bodies, who assess technical competence of laboratories, should select and use proficiency testing schemes.

This part of lSO/IEC Guide 43 is intended for use by proficiency testing operators and users such as participant laboratories, accreditation bodies, regulatory authorities and clients of laboratory services who have a need to assess the technical competence of laboratories.

It is particularly useful for laboratories in self-valuation, but recognizes that proficiency testing is only one mechanism which can contribute to the establishment of mutual confidence between users of different testing laboratories.

It is currently a condition of some accreditation bodies that laboratories participate regularly in proficiency testing schemes that they have accepted as fit for purpose. Therefore, it is essential that operators of such schemes comply with principles for conduct of professionally managed proficiency schemes, both in terms of technical requirements, statistical procedures (see examples in annex A), and in quality management (see guidance in annex B).

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 comparisons. The contents of this Guide are intended only as a framework to be modified appropriately for particular situations, including schemes with either small or large numbers of participants.

This Guide is not intended to cover a technique often used by organizations to evaluate a single laboratory's performance through submissions of certified reference materials or other well characterized test items.

A bibliography is given in annex C.