Traceability and its role in interlaboratory comparisons (proficiency testing programmes), modeled on trace element determination in biological materials

Traceability is not always evident in proficiency testing programs, althoug h this is a requirement in ISO/IEC Guide 43-1. The assigned, or "true", val ue in most programs is not traceable to an independent entity. The test mat erials should generally be similar in nature to those routinely tested by p articipating laboratories. This is far from always the case and it is impor tant to realize that if the difference is large, there may be no traceabili ty to the testing program. It is also important that results from participa tion in proficiency tests are cited when papers are published, in order to enhance reliability/credibility of the published data.