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arXiv 1810.13402stat.ME
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由于选择导致的边界偏倚

Bounding bias due to selection

Louisa H. Smith, Tyler J. VanderWeele

摘要:

当流行病学研究是在人群的一个子集中进行时,选择偏倚会威胁到因果推断的有效性。无论所选人群是否为目标人群,这种偏倚都可能发生,甚至在不存在确定性-结果混杂的情况下也可能发生。然而,通常很难量化选择偏倚的程度,而且敏感性分析也很难进行和理解。在这篇文章中,我们证明,由于选择的偏差的大小可以由简单的表达式定义的参数表征的未测量的因素(S)负责的偏差和测量变量之间的关系。对于这些不可测量的因素,没有必要进行函数形式的假设。利用有关选择机制的知识,研究人员可以通过指定界限中参数的大小来解释选择偏差的可能程度。我们还表明,界限,这取决于目标人群不同,导致汇总措施,可用于计算所需的参数的最小幅度的风险比为零。概括性度量可用于确定解释一个结果所必需的选择的总体强度。然后,我们表明,在某些情况下,或与某些假设的界限和汇总措施可以简化。使用不同的选择机制的例子,我们还演示了研究人员如何实现这些简单的敏感性分析。

英文摘要:

When epidemiologic studies are conducted in a subset of the population, selection bias can threaten the validity of causal inference. This bias can occur whether or not that selected population is the target population, and can occur even in the absence of exposure-outcome confounding. However, it is often difficult to quantify the extent of selection bias, and sensitivity analysis can be challenging to undertake and to understand. In this article we demonstrate that the magnitude of the bias due to selection can be bounded by simple expressions defined by parameters characterizing the relationships between unmeasured factor(s) responsible for the bias and the measured variables. No functional form assumptions are necessary about those unmeasured factors. Using knowledge about the selection mechanism, researchers can account for the possible extent of selection bias by specifying the size of the parameters in the bounds. We also show that the bounds, which differ depending on the target population, result in summary measures that can be used to calculate the minimum magnitude of the parameters required to shift a risk ratio to the null. The summary measure can be used to determine the overall strength of selection that would be necessary to explain away a result. We then show that the bounds and summary measures can be simplified in certain contexts or with certain assumptions. Using examples with varying selection mechanisms, we also demonstrate how researchers can implement these simple sensitivity analyses.

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