Repeatability of paired counts
Repeatability of paired counts
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DOI：
10.1002/sim.2724
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发表时间：
2007-08-30
影响因子：
2
通讯作者：
Brooker, Simon
中科院分区：
文献类型：
--
作者：
Alexander, Neal;Bethony, Jeff;Brooker, Simon
Bland和Altman技术广泛用于评估临床测量方法重复测定之间的变异。它产生重复性，即95%的重复测量值。该技术的有效使用要求方差在数据范围内是恒定的。对于CD 4细胞或寄生虫等项目的计数，通常情况并非如此，对数转换也不适用于零计数。研究了基于Box-Cox变换的广义差分的性质。例如，在一个数据集的钩虫卵计数的加藤-卡茨方法，平方根变换被发现稳定的方差。我们展示了如何将平方根尺度上的可重复性反向转换为计数本身的可重复性，作为卵计数平方根均值的递增函数，即平方根均值的平方。不仅更容易解释，反转换结果还突出了重复性对所用样品体积的依赖性。版权所有（c）2006约翰威利父子有限公司。
The Bland and Altman technique is widely used to assess the variation between replicates of a method of clinical measurement. It yields the repeatability, i.e. the value within which 95 per cent of repeat measurements lie. The valid use of the technique requires that the variance is constant over the data range. This is not usually the case for counts of items such as CD4 cells or parasites, nor is the log transformation applicable to zero counts. We investigate the properties of generalized differences based on Box-Cox transformations. For an example, in a data set of hookworm eggs counted by the Kato-Katz method, the square root transformation is found to stabilize the variance. We show how to back-transform the repeatability on the square root scale to the repeatability of the counts themselves, as an increasing function of the square mean root egg count, i.e. the square of the average of square roots. As well as being more easily interpretable, the back-transformed results highlight the dependence of the repeatability on the sample volume used. Copyright (c) 2006 John Wiley & Sons, Ltd.