Spearman-Brown prophecy formula and Cronbach's alpha: different faces of reliability and opportunities for new applications
Spearman-Brown prophecy formula and Cronbach's alpha: different faces of reliability and opportunities for new applications
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DOI：
10.1016/j.jclinepi.2017.01.013
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发表时间：
2017-05-01
影响因子：
7.2
通讯作者：
Terwee, Caroline B.
中科院分区：
文献类型：
--
作者：
de Vet, Henrica C. W.;Mokkink, Lidwine B.;Terwee, Caroline B.
目的：不同形式的可靠性之间存在相似之处，例如内部一致性（内部可靠性）以及评价者间和评价者内的可靠性。基于经典测试理论的可靠性系数可以表示为组内相关系数（ICC），例如Cronbach's alpha。采用斯皮尔曼布朗预测公式（SB公式）计算问卷项目数变化时的信度。本文旨在通过指出可靠性系数的假设，各种系数之间的相似性，以及随后的新应用的可靠性coefficients.Design，设置和结果：Cronbach的α和SB公式的起源和假设进行了讨论，以增加对可靠性研究的了解。Cronbach's alpha是一个ICC公式，使用了一个众所周知的属性，即取多个评级的平均值可以增加测量的可靠性。我们用一个例子说明，ICC公式的平均测量的多个评分员和SB公式给出了类似的结果。这意味着SB公式可用于决定要取平均值的测量值数量，从而决定所需的评分者数量，以获得具有可接受可靠性的测量值，即使ICC公式的方差分量未知。使用相同的例子，我们说明的原则，“克朗巴赫的阿尔法，如果项目删除”，以决定最差的性能raters.Conclusion：这些应用程序有不同的假设：“克朗巴赫的阿尔法，如果项目删除”的原则是基于一个固定的项目/评分者的假设和SB公式是基于随机的评分者的假设。这个例子还强调了需要更多的评分员在设计的可靠性研究，以获得可靠性的稳健估计。(C)2017爱思唯尔公司All rights reserved.
Objectives: There are similarities between the different forms of reliability, such as internal consistency (internal reliability) and interrater and intrarater reliability. Reliability coefficients that are based on classical test theory can be expressed as intraclass correlation coefficients (ICCs), such as Cronbach's alpha. The Spearman Brown prophecy formula (SB formula) is used to calculate the reliability when the number of items in a questionnaire is changed. This paper aims to increase insight into reliability studies by pointing to the assumptions of reliability coefficients, similarities between various coefficients, and the subsequent new applications of reliability coefficients.Design, Settings and Results: The origin and assumptions of Cronbach's alpha and the SB formula are discussed. Cronbach's alpha is written as an ICC formula, using the well-known property that taking the average value of a number of ratings increases the reliability of a measurement. We illustrate with an example that the ICC formulas for average measurements of multiple raters and the SB formula give similar results. This implies that the SB formula can be used to decide on the number of measurements to be averaged and thus on the number of raters required, for obtaining measurements with acceptable reliability, even if the variance components of the ICC formula are not known. Using the same example, we illustrate the principle of "Cronbach's alpha if item deleted" to decide on the poorest performing raters in a set of raters.Conclusion: These applications have different assumptions: the principle of "Cronbach's alpha if item deleted" is based on the assumption of a fixed set of items/raters and the SB formula is based on the assumption of random raters. The example also emphasizes the need for more raters in the design of the reliability study to obtain a robust estimation of reliability. (C) 2017 Elsevier Inc. All rights reserved.