Within-Laboratory Variance Outlier Detection: An Alternative to Cochran’s Test

Q3 Agricultural and Biological Sciences
M. Morton
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Abstract

Summary An important step in the full definition of an analytical method is the characterization of the within and between laboratory variability. This is typically done through collaborative studies involving multiple laboratories. The statistical analysis of the results of collaborative studies is generally carried out using standardized protocols such as those given in ISO 5725-2 or ASTM E691-14. One aspect of the evaluation of collaborative studies is the identification of outlying laboratories which are then excluded from the variance calculation associated with the analytical method. Whether particular laboratories are identified as outliers can have a dramatic effect on the calculated variances. The generally recommended approach to identify laboratories with excessive within-laboratory variation is Cochran’s Test or something similar. However, Cochran’s Test is very sensitive to non-normality of the underlying statistical distribution. When the assumption of normality is violated, Cochran’s Test can wrongly identify laboratories as outliers at much greater than the nominally stated error rate, even for deviations from normality that are very difficult to detect analytically. In this paper, an alternative to Cochran’s Test, adapted from Levene’s Test, is proposed and shown to approximately maintain the stated error rate when the underlying distribution is not normal. This newly adapted test is recommended for future collaborative study analysis in place of Cochran’s Test.
实验室内方差异常值检测:科克伦检验的替代方法
全面定义分析方法的一个重要步骤是描述实验室内部和实验室之间的变异性。这通常是通过涉及多个实验室的合作研究来完成的。合作研究结果的统计分析通常使用标准化协议进行,例如ISO 5725-2或ASTM E691-14中给出的协议。评估合作研究的一个方面是确定外围实验室,然后将其排除在与分析方法相关的方差计算之外。特定实验室是否被认定为异常值会对计算的方差产生巨大影响。一般推荐的方法来识别实验室内部变异过多的实验室是科克伦测试或类似的东西。然而,科克伦检验对基础统计分布的非正态性非常敏感。当正态假设被违反时,科克伦检验可以错误地将实验室识别为异常值,其错误率远远大于名义上声明的错误率,甚至对于很难通过分析检测到的偏离正态的实验室也是如此。在本文中,提出了一种替代Cochran检验的方法,改编自Levene检验,并证明了当底层分布是非正态分布时,它可以近似地保持规定的错误率。这个新调整的测试被推荐用于未来的合作研究分析,以取代科克伦测试。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Beitrage zur Tabakforschung International/ Contributions to Tobacco Research
Beitrage zur Tabakforschung International/ Contributions to Tobacco Research Agricultural and Biological Sciences-Agronomy and Crop Science
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