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Clinical Chemistry and Laboratory Medicine (CCLM)

Published in Association with the European Federation of Clinical Chemistry and Laboratory Medicine (EFLM)

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Ed. by Gillery, Philippe / Lackner, Karl J. / Lippi, Giuseppe / Melichar, Bohuslav / Payne, Deborah A. / Schlattmann, Peter / Tate, Jillian R.

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Impact of a common CV evaluation scheme on overall laboratory performance: 8-year experience of a large national proficiency testing program in Japan

Kiyoshi Ichihara1 / Tadashi Kawai2



Corresponding author: Kiyoshi Ichihara, MD, PhD, Department of Clinical Laboratory Sciences, Faculty of Health Sciences, Yamaguchi University School of Medicine, Minami-Kogushi 1-1-1, Ube, 755-8505 Japan Phone/Fax: +81-836-22-2884,

Citation Information: Clinical Chemical Laboratory Medicine. Volume 43, Issue 4, Pages 422–430, ISSN (Online) 1437-4331, ISSN (Print) 1434-6621, DOI: 10.1515/CCLM.2005.075, April 2005

Publication History

August 27, 2004
January 26, 2005


In proficiency testing (PT), it is difficult to set rational criteria for determining target values and allowable limits. In Japan, the largest national PT program has for the past 8 years used an evaluation scheme based on a “common coefficient of variation” (cCV) to overcome this difficulty. The cCV, the average within-method variation, is derived by one-way analysis of variance from data of peer groups after excluding those with large variations. A unit interval used for grading participants is obtained by multiplying the cCV by the peer-group mean which is computed using an iterative method featuring repeated removal of a large portion of the tails of the distribution and reinflation of the standard deviation (SD) to compensate for the trimming. The evaluation scheme gives a relatively better grade to those participants in peer groups with small CVs, compared to use of individual peer-group CVs. The scheme has expedited the transition to more reproducible methods, resulting in a notable overall improvement in laboratory performance. The cCV evaluation scheme is uniformly applicable to any analyte measured quantitatively. The iterative method, an integral part of the scheme, effectively precludes bias in the evaluation.

Keywords: between-method coefficient of variation; iterative method; proficiency testing; target value; within-method coefficient of variation

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