COMPARISON OF DIFFERENT APPROACHES TO EVALUATE PROFICIENCY TEST DATA

摘要

Proficiency testing (PT) is an essential tool for assessing the competency of analyticallaboratories. Proficiency testing involves the regular circulation of test materials for analysis by the participating laboratories, and the subsequent assessment of the resulting data by the organizing body. To this end, several rating systems have been developed for determining a laboratory's performance. The z-scores and u-scores are the most frequently used evaluation approaches, each having its own specifics. By using the z-score the accuracy of participants' results will be evaluated, while using the u-score uncertainties of the participant measurement results and the uncertainty of the assigned PT value are also taken into consideration. Consequently, evaluations of laboratories using the z-score will not necessarily exhibit the same level of performance as in the cases of evaluations using the u-score, where also the measurement uncertainties are considered in the evaluation. The IAEA Reference Material Group in Seibersdorf, Austria uses a modified u-score evaluation system, thus taking into consideration the trueness and the precision of the reported data and it includes in the evaluation both the total combined uncertainty associated with the target value of proficiency testing samples and the total uncertainty reported by the participating laboratories. A set of data for determination of ~(57)Co in spiked soil material from a proficiency test performed by the IAEA Reference Material Group in Seibersdorf was used to compare different rating systems.