The assessment of the QUASIMEME laboratory performance studies data: Techniques and approach

A detailed assessment programme has been developed by the QUASIMEME Scientific Assessment Group to evaluate the results of the five rounds of the interlaboratory studies for the main mandatory chemical determinands in European Marine Monitoring Programmes. Two robust statistical algorithms were evaluated and one applied systematically to the study data. The established method of evaluation dealt with zero values, ‘less than’ values, skewed distributions, bimodal distributions from methodologically defined measurements and extreme values differing by factors of 2 to 1000 from the assigned value. Data from reference laboratories and declared concentrations from the sample preparation were, in the main, used to establish the assigned values. Z Scores were used to assess the laboratory performance. The sum of the number of satisfactory Z scores was used as an indicator of performance for successive inter-laboratory studies.