Zeta scores

En numbers are used when the assigned value has been produced by a reference laboratory, which has provided an estimate of the expanded uncertainty. This scoring method also requires a valid estimate of the expanded uncertainty for each participant s result. A score of En < 1 is considered satisfactory. The acceptability criterion is different from that used for z-, z - or zeta-scores as En numbers are calculated using expanded uncertainties. However, the En number is equal to zeta/2 if a coverage factor of 2 is used to calculate the expanded uncertainties (see Chapter 6, Section 6.3.6). En numbers are not normally used by proficiency testing scheme providers but are often used in calibration studies. 

AMC (2000) How to combine proficiency test results with your own uncertainty estimate - the zeta score. AMC Technical Brief No. 2 (Nov 2000). Analytical Methods Committee, Royal Society of Chemistry, London, 2 pp. 

The zeta scores issued to IMEP participants are based on single performance statistics, accounting for an extended uncertainty wext of the CRV as well as the reported uncertainty of the participant s measurement result. When calculating zeta -scores according to Equation (7.2), the measurement performance indicators for zeta -scores can be aligned with those of the corresponding z-scores. In case an IMEP participant does not report an uncertainty, the zeta -number equals the z-score zeta < 2 satisfactory 2 < zeta < 3 questionable zeta > 3 unsatisfactory. 

While evaluating the laboratory performance according to ISO/DIS 13528, the probciency test provider computes a normalized bias, which is the difference between the participant s reported measurement result and a reference value divided by a normalization factor [67]. The z-score and the zeta -scores are the two scoring equations presented earlier in Section 7.3.1. The ISO/IEC Guide 43 requires that the PT provider clearly states the applied performance criteria and how they were derived [37]. 

Soil samples spiked with c at approximately 100 Bq kg were processed through the method described in section 2.3 in six different analytical batches. Results (Table 3) were compared using the zeta test. Results for which the absolute value of the zeta score was less than 2.576 were considered to be in agreement. 

Sample ID Measnned Valne /Bqkg Reference Value /Bqkg Zeta Score In Agreement ... 

Zeta (z) scores are commonly used as a performance indicator in PT schemes [37, 61, 62]. Sometimes, a consensus value derived from participants results can serve as reference and the performance criteria, sometimes called target value, equals one standard deviation. This means that 95 percent of the participants would automatically report satisfactory results. In IMEP a z-score is meant as ... 

As a commercial company that provides analytical services for the determination of radionuclides for a wide variety of clients, AMEC required a more accurate and reliable method to be developed. It needed to use relatively low hazard chemicals, have improved accuracy and precision and utilise common radiochemical analytical laboratory equipment such as liquid scintillation counters and gravity fed chromatography columns. In addition, the process must have realistic and commercially viable batch sizes, operator time and turnaround times, so that samples can be analysed in a cost-effective manner. Ideally the whole process for a batch of samples should not exceed more than one working week. As part of the validation process both internal and external quality control (QC) samples were used along with statistical tests, such as zeta (Q scores and student t-tests , to determine the accuracy of the improved method. In addition, elution profiles for iodine and chlorine and decontamination tests for potentially interfering radionuclides were also carried out in order to further validate the process. 

Sample ID Re Recovery /% Tc Recovery /% Zeta, In Agreement Score ... 

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