Assessing laboratory performance in intercomparisons for inorganic analysis

This review addresses the assessment of laboratory performance in intercomparisons for inorganic analysis. Three types of intercomparisons in question are proficiency testing schemes, measurement evaluation programs, and international key comparisons. Evaluation of intercomparisons focuses primarily on purposes of participation, participants involved, sample matrices encountered, methods commonly used for analysis, traceability of assigned values to SI, calculation of performance statistics, reporting of measurement uncertainty, and multimodality. We discuss trends towards using SI-traceable reference values in assessing laboratory performance, reporting measurement uncertainty for comparability purposes, and using multiple statistics (e.g., z-scores, En numbers and zeta-scores) as indicators of laboratory performance.