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Quality control charts for short or long runs without a training phase. Part 1. Performances in state of control and in the presence of outliers

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Abstract

Sometimes analytical laboratories receive requests with a small number of determinations and/or a small number of samples, or outside the typical scope of analytical services. As a result, they may not have historical data on the performance of analytical processes and/or appropriate reference materials. Under these conditions it is difficult or uneconomical to use traditional or classic quality control charts. This is the so-called start-up problem of these charts. The Q charts seem appropriate charts under these conditions because they do not need any prior training or study phase. The fundamentals and the algebraic expressions of Q charts for the mean (four cases) and for the variance (two cases) are offered. This experimental study of Q charts for individual measurements was done with data from quality control for the evaluation of mass fraction of Ni and Al2O3 in a laterite CRM by ICP-OES. The performance of these Q charts is discussed where the analytical process is in the state of statistical control and in the presence of outliers at the start-up. In the first situation performance of Q charts are quite satisfactory and they behave properly. When outliers are collected at the beginning, the deformation of some charts is evident or the charts become useless. Severe outliers will corrupt the parameter estimates and the subsequent plotted points, or the charts will become insensitive and useless. The practitioner should take extreme care to assure that the initial values are obtained in the state of statistical control to have adequate sensitivity to detect parameter shifts.

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Authors and Affiliations

  1. Faculty of Chemistry, University of Havana, Cuba. Zapata y G, S/N, La Habana, Cuba

    Manuel Alvarez-Prieto

  2. Central Laboratory José I. del Corral, Institute of Geology and Paleontology, Ministry of Energy and Mines, Carretera Central y Vía Blanca No. 1002, La Habana, Cuba

    Ricardo S. Páez-Montero

Authors
  1. Manuel Alvarez-Prieto
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  2. Ricardo S. Páez-Montero
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Contributions

Both authors contributed to the study, conception and design of this article. Material preparation, data collection and analysis were performed by Manuel Alvarez-Prieto and Ricardo Páez-Montero. The first draft of the manuscript was written by Manuel Alvarez-Prieto and the coauthor commented on previous versions of the manuscript and the final one. Both authors read and approved the final manuscript.

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Correspondence to Manuel Alvarez-Prieto.

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Alvarez-Prieto, M., Páez-Montero, R.S. Quality control charts for short or long runs without a training phase. Part 1. Performances in state of control and in the presence of outliers. Accred Qual Assur (2024). https://doi.org/10.1007/s00769-024-01584-z

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