Regulatory aspects of proficiency testing: experience from the water sector

Proficiency tests in the regulated sector have requirements different from other areas. Repeated unsuccessful participation can lead to the economic ruin of a laboratory. This is illustrated at the water analyses sector in Germany as an example. Collusion and falsification have to be avoided. A special and uniform evaluation technique is necessary that includes the possibility of a common evaluation of different concentration levels and considers the skewed distribution of data. A suitable approach is published in a new German DIN standard (DIN 38402-45). The assessment of the values and the laboratories as a whole also needs special attention. A concept to do this with as few injustices as possible was developed in an inter-state working group in Germany.