Proficiency Testing performance measures scores

Participation in proficiency testing schemes is an ongoing activity. It is therefore useful to monitor performance over a period of time and to look for trends. Performance over time can be demonstrated statistically by using measures such as RSZ and SSZ (see Section 7.3.4) but as mentioned previously, these can be misleading. It is better to monitor performance scores by plotting them on a... 

Participation in proficiency tests is not a prerequisite or an absolute substitute for IQC measures or vice versa. However, participance in proficiency tests is meaningless without a well-developed IQC system. IQC underlies participance in PT schemes, while IQC and participance in PT schemes are both important substitutes of AQA (Figure 6). It is shown that laboratories with the strongest QC procedures score significantly better in PT schemes [8,50]. Participance in PT can to a certain extent improve the laboratory s performance however unsatisfactory performance in schemes (up to 30% of all participants) has been reported. This means that there... 

The variation of sensitivity between different sensors was also checked. Calibration curves with five different sensors were performed. A Relative Standard Deviation of 13, 13 and 42% of calibration slopes (sensitivity) were obtained for Cu, Pb and Cd respectively. These variations should have limited consequence on bias and precision when the standard addition method is used. However, for Cd, variations in the limit of quantification between two electrodes could be expected. Finally, the accuracy of the method was evaluated by the measurement of a SWIFT reference material used during the 2nd SWIFT-WFD Proficiency Testing exercise (Table 4.2.2). The reference value was chosen as the consensus value of the selected data population obtained after excluding the outliers. The performances of the device were estimated according to the Z-score (Z) calculation. Based on this score, results obtained with the SPEs/PalmSens method were consistent with those obtained by all methods for Pb and Cu ( Z < 2) while the result was less satisfactory for Cd (2 < Z < 3). 

---