LAUSR

Conducting proficiency tests with large numbers of participants are not a problem because the ISO standard 13528:2015 describes many indicators that allow for proper assessment. However, there are proficiency testing (PT) schemes that involve only few participants. In such situations, the same difficulties exist for the selection of proper indicators and the criteria for assessing the participants' achievements. The Institute for Chemical Processing of Coal in Zabrze, Poland organised a round of PT of the determination of gypsum parameters. The results from six participants from Polish research entities and independent laboratories and methodology for the organisation this PT are presented. The performance evaluation criteria were determined using participants results due to the inability to use the metrologically valid procedure. The performance of the participants was evaluated using z′ and zeta scores.