Many types of civil unrest, including protest, violent conflict, and rebellion, have been found to be subject to both inter- and intra-state contagion. These spillover effects are conventionally tested through the application of parametric structural models that are estimated using observational data. Drawing on research in methods for network analysis, we note important challenges in conducting causal inference on contagion effects in observational data. We review a recently developed non-parametric test—the “split-halves test”—that is robust to confounding and apply the test to replication data from several recent studies in which researchers tested for contagion in civil unrest. We find that about half the time findings in the published literature fail to replicate with the split-halves test. Across ten total replications, we do not see strong patterns in terms of which results do and do not replicate. We do, however, find evidence for general contagion in six of the replications, indicating that contagion is a prevalent phenomenon in civil unrest. As such, we recommend that researchers (1) use the split-halves test as a general-purpose robustness check for parametric models of contagion in the study of civil unrest, and (2) consider modeling contagion in research on civil unrest.

中文翻译：

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传染性内乱理论的因果证据


许多类型的内乱，包括抗议、暴力冲突和叛乱，已被发现受到国家间和国家内部的传染。这些溢出效应通常通过应用使用观测数据估计的参数化结构模型来测试。借鉴对网络分析方法的研究，我们注意到对观测数据中的传染效应进行因果推断的重要挑战。我们回顾了最近开发的一种非参数检验——“split-halfves 检验”——它对混淆很稳健，并将该检验应用于最近几项研究的复制数据，在这些研究中，研究人员测试了内乱中的传染性。我们发现，已发表文献中大约一半的时间发现无法通过分裂半部检验进行复制。在总共 10 个重复中，我们没有看到关于哪些结果可以重复和不重复的强烈模式。然而，我们确实在其中 6 个重复中发现了普遍传染的证据，这表明传染是内乱中普遍存在的现象。因此，我们建议研究人员 （1） 在内乱研究中使用分裂半检验作为传染参数模型的通用稳健性检查，以及 （2） 考虑在内乱研究中对传染进行建模。