AI 中文总结
研究针对因果中介分析中反悔孪生路径特定效应，推导其与自然PSEs绝对差异的上下界，通过模拟研究评估二者在非线性等场景下符号和排序的不一致频率，发现受中间混杂因素相关性影响，解释时需谨慎，为后续确定一致结论条件提供方向。
AI 中文摘要
最近提出的反悔孪生路径特定效应框架用于解决因果中介分析中的中间混杂问题，能将平均治疗效应分解为可识别的细粒度路径特定效应（PSEs）。然而，一个未解决的问题是反悔孪生PSEs在多大程度上反映其相应自然PSEs的方向和相对大小。本文系统地从大小、符号和排序方面刻画了反悔孪生PSEs的行为，并与自然PSEs进行基准比较。首先在二元结果设置中推导了反悔孪生和自然PSEs绝对差异的非参数、可识别的上下界。然后进行模拟研究评估非线性、非单调场景中反悔孪生和自然效应在符号和排序上的不一致频率。发现在四种场景和320个数值设置下，排序不一致率为15%至56%，符号不一致率为5%至43%。不一致受中间混杂因素反事实值之间不可观察的相关性强烈影响。这表明在解释反悔孪生PSEs的大小和排序时需谨慎，并推动未来工作确定在非单调性存在时两种类型PSEs得出一致结论的条件。
英文摘要
The framework of recanting twin path-specific effects has recently been propose to address the issue of intermediate confounding in causal mediation analysis, enabling the decomposition of the average treatment effect into identifiable fine-grained path-specific effects (PSEs). An open question, however, is the extent to which recanting-twin PSEs reflect the direction and relative magnitude of their corresponding natural PSEs. In this paper, we systematically characterize the behaviors of the recanting-twin PSEs in terms of magnitude, sign and ranking, benchmarking against natural PSEs. To achieve this, we first derive non-parametric, identifiable upper and lower bounds for the absolute difference between recanting-twin and natural PSEs in binary outcome settings. These bounds provide a practical way to assess whether discrepancies in magnitude between the two types of effects are substantial, thereby facilitating the use of recanting-twin PSEs as informative approximations of their natural counterparts. A simulation study is then conducted to evaluate frequency of disagreements in sign and ranking between recanting-twin and natural effects in non-linear, non-monotonic scenarios. Across four scenarios and 320 numerical settings, we find that disagreement ranges from 15% to 56% for ranking and from 5% to 43% for sign. Disagreement is strongly influenced by the non-observable correlation between counterfactual values of the intermediate confounder, suggesting that caution is needed when interpreting the magnitude and ranking of recanting-twin PSEs, and motivating future work to identify conditions under which the two types of PSEs yield consistent conclusions when non-monotonicity presents.
