Objectives

Review causal mediation analysis as a method for estimating and assessing direct and indirect effects. Re-examine a field experiment with an apparent implementation failure. Test procedural justice theory by examining to which extent procedural justice mediates the impact of contact with the police on police legitimacy and social identity.

Methods

Data from a block-randomised controlled trial of procedural justice policing (the Scottish Community Engagement Trial) were analysed. All constructs were measured using surveys distributed during roadside police checks. Treatment implementation was assessed by analysing the treatment effect’s consistency and heterogeneity. Causal mediation analysis, which can derive the indirect effect even in the presence of a treatment–mediator interaction, was used as a versatile technique of effect decomposition. Sensitivity analysis was carried out to assess the robustness of the mediating role of procedural justice.

Results

First, the treatment effect was fairly consistent and homogeneous, indicating that the treatment’s effect is attributable to the design. Second, there is evidence that procedural justice channels the treatment’s effect towards normative alignment (NIE = − 0.207), duty to obey (NIE = − 0.153), and social identity (NIE = − 0.052), all of which are moderately robust to unmeasured confounding (ρ = 0.3–0.6, LOVE = 0.5–0.7).

Conclusions

The effect’s consistency and homogeneity should be examined in future block-randomised designs. Causal mediation analysis is a versatile tool that can salvage experiments with systematic yet ambiguous treatment effects by allowing researchers to “pry open” the black box of causality. The theoretical propositions of procedural justice policing were supported. Future studies are needed with more discernible causal mediation effects.

中文翻译：

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揭开因果关系的黑匣子：程序正义警务的因果中介分析检验

目标

将因果中介分析作为一种估计和评估直接和间接影响的方法。重新检查具有明显实施失败的现场实验。通过检查程序正义在多大程度上调解了与警察接触对警察合法性和社会认同的影响，从而检验了程序正义理论。

方法

分析了程序正义警务的一项随机分组对照试验（苏格兰社区参与试验）的数据。使用路边警察检查期间分发的调查来测量所有构造。通过分析治疗效果的一致性和异质性来评估治疗的实施。因果中介分析（即使在存在治疗与介体相互作用的情况下也可以得出间接影响）被用作影响分解的通用技术。进行了敏感性分析，以评估程序正义的调解作用的稳健性。

结果

首先，治疗效果相当一致且均匀，表明治疗效果可归因于设计。其次，有证据表明，程序正义将治疗的效果引导至规范统一（NIE = − 0.207），服从义务（NIE = − 0.153）和社会认同（NIE = − 0.052），所有这些因素对未测度都具有中等强度混杂（ρ= 0.3–0.6，LOVE = 0.5–0.7）。

结论

在将来的块随机设计中，应检查效果的一致性和同质性。因果中介分析是一种多功能工具，可以通过允许研究人员“撬开”因果关系的黑匣子来挽救具有系统性但模棱两可的治疗效果的实验。支持程序正义警务的理论主张。需要进一步研究因果关系的影响。