Abstract
The S-score is a new performance score applicable to proficiency testing (PT) for binary data. It allows the proficiency test provider to choose how the assigned value (AV) is defined, e.g., positive versus negative, either by the PT provider or by laboratory consensus based on participating laboratories. It is a flexible tool that can be used to select as a maximum four types of proficiency test items (PTIs) depending on the required correct results and expected correct results predefined by the PT provider. Regarding the required correct results, for an easy tasks, e.g., easy analyte detection, correct results matching with the assigned value are required for all PTI1s. For difficult tasks, e.g. close to the limit of detection (LOD) with replicated samples and for mixed tasks with unreplicated, an acceptable range of correct results is required using the binomial probability density from at least six PTI2s. Regarding correct results expected but not required for difficult tasks, results matching with the assigned value are requested by the PT provider for all PTI3s and by a participating laboratory consensus (LC) for all PTI4s. The S-score was designed as a numerical indicator taking into account all the combinations of the different types of PTIs. The decimal part summarizes the laboratory results indicating the rate of incorrect results in relation to the different PTIs assigned values. The integer part provides a similar interpretation to the one of the z-score for quantitative PT, with ‘satisfactory’ (1 ≤ S-score < 2), ‘questionable’ (2 ≤ S-score < 3), and ‘unsatisfactory’ (S-score ≥ 3) performance, respectively.
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Acknowledgements
This work was initiated as part of the revision of the ANSES methodological and statistical Proficiency Testing guide undertaken by an ANSES working group, where this tool was presented and discussed. It was conducted in close collaboration with ANSES PT coordinators. We would like to thank for their active participation Myriam Thomas, Sylvie Hénault, Aurore Romey, and Carine Paraud (animal health); Laetitia Bonifait and Florence Guiller (food microbiology), as well as the members of the ANSES working group: Stéphanie Bougeard, Aude Chabirand, Maud Marsot, Jean-Sébastien Py, Jean-Luc Schereffer, and Catherine De Meredieu. The authors wish to thank Marc Tabouret and Thierry Dupont for the reading and helpful comments.
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1-2-4-5-6 wrote the main manuscript, 1-3-6 Designer of score, 1-3-5-6 developed mathematical approach, 1-2-5-6 prepared figure, all authors participated for tables, and all authors have reviewed the manuscript
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Baudry, C., Jadé, G., Rayneau, P. et al. S-score: a new score for binary qualitative proficiency testing schemes interpretable as the z-score. Accred Qual Assur 29, 103–113 (2024). https://doi.org/10.1007/s00769-023-01561-y
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DOI: https://doi.org/10.1007/s00769-023-01561-y