Comparison of different statistical approaches used to evaluate the performance of participants in a proficiency testing program

Oliveira, Camila Cardoso deTiglea, PauloOliveira, José CarlosCarvalho, Maria de Fátima HenriquesBuzzo, Márcia LianeSakuma, Alice MomoyoDuran, Maria CristinaCaruso, Miriam Solange FernandesGranato, Daniel

Five statistical approaches were applied for assessing the performance of participants in 19 rounds(2007-2011) of the Proficiency Testing Program for lead in blood determination (PEP-Pbs), conducted by Instituto Adolfo Lutz. The performance evaluation was provided by using the z-score. The following statistical approaches were tested: 1 – mean and standard deviation, after rejecting outliers; 2 – median and normalized inter-quartile range; 3 – robust mean and robust standard deviation; 4 – robust meanand standard deviation for proficiency assessment of 3 μg/100 mL (for concentrations up to 40 μg/100mL and a standard deviation for proficiency assessment of 7.5 % of the assigned value (for concentrations above 40 μg/100 mL); 5 – robust mean and standard deviation for proficiency assessment of 2 μg/100 mL(for concentration up to 40 μg/100 mL) or 5 % of the assigned value (for concentrations above 40 μg/100mL). The approach 4 showed to be the most adequate statistical methodology to assess the performance of participating laboratories in the PEP-Pbs...

1. statistical techniques
2. z-score
3. inter-laboratory comparison programs
4. proficiency testing program