Article (Scientific journals)
Comparison of different approaches to evaluate External Quality Assessment Data.
Coucke, Wim; China, Bernard; Delattre, Isabelle et al.
2012In Clinica Chimica Acta, 413 (5-6), p. 582-6
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Abstract :
[en] In EQA programs, Z-scores are used to evaluate laboratory performance. They should indicate poorly performing laboratories, regardless of the presence of outliers. For this, two different types of approaches exist. The first type are "outlier-based" approaches, which first exclude outlying values, calculate the average and standard deviation on the remaining data and obtain Z-scores for all values (e.g., Grubbs and Dixon). The second type includes the "robust" approaches (e.g., Tukey and Qn or the algorithm recommended by ISO). The different approaches were assessed by randomly generated samples from the Normal and Student t distributions. Part of the sample data were contaminated with outliers. The number of false and true outliers was recorded and subsequently, Positive and Negative Predictive Values were derived. Also, the sampling mean and variability were calculated for location and scale estimators. The various approaches performed similarly for sample sizes above 10 and when outliers were at good distance from the centre. For smaller sample sizes and closer outliers, however, the approaches performed quite differently. Tukey's method was characterised by a high true and a high false outlier rate, while the ISO and Qn approaches demonstrated weak performance. Grubbs test yielded overall the best results.
Disciplines :
General & internal medicine
Author, co-author :
Coucke, Wim
China, Bernard
Delattre, Isabelle
Lenga, Yolande
Van Blerk, Marjan
Van Campenhout, Christel
Van de Walle, Philippe
Vernelen, Kris
Albert, Adelin  ;  Université de Liège - ULiège > Département des sciences de la santé publique > Informatique médicale et biostatistique
Language :
English
Title :
Comparison of different approaches to evaluate External Quality Assessment Data.
Publication date :
2012
Journal title :
Clinica Chimica Acta
ISSN :
0009-8981
eISSN :
1873-3492
Publisher :
Elsevier Science, Amsterdam, Netherlands
Volume :
413
Issue :
5-6
Pages :
582-6
Peer reviewed :
Peer Reviewed verified by ORBi
Commentary :
Copyright (c) 2011 Elsevier B.V. All rights reserved.
Available on ORBi :
since 19 September 2012

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