Procedural justice theory and the black box of causality

This thesis makes a theoretical and a methodological contribution. Theoretically, it tests certain predictions of procedural justice policing, which posits that neutral, fair, and respectful treatment by the police is the cornerstone of fruitful police-public relations, in that procedural justice leads to increased police legitimacy, and that legitimacy engenders societally desirable outcomes, such as citizens’ willingness to cooperate with the police and compliance with the law. Methodologically, it identifies and assesses causal mechanisms using a family of methods developed mostly in the field of epidemiology: causal mediation analysis. The theoretical and methodological aspects of this thesis converge in the investigation of (1) the extent to which procedural justice mediates the impact of contact with the police on police legitimacy and psychological processes (Paper 1), (2) the mediating role of police legitimacy on willingness to cooperate with the police and compliance with the law (Paper 3, Paper 4), and (3) the psychological drivers that channel the impact of procedural justice on police and legal legitimacy (Paper 2). This thesis makes use of a randomised controlled trial (Scottish Community Engagement Trial), four randomised experiments, and one experiment with parallel (encouragement) design on crowdsourced samples from the US and the UK (recruited through Amazon Turk and Prolific Academic). The causal evidence attests to the centrality of procedural justice, which mediates the impact of an encounter with the police on police legitimacy, and influences psychological processes and police legitimacy. Personal sense of power, not social identity, is the causal mediator of the effect of procedural justice on police and legal legitimacy. Finally, different aspects of legitimacy transmit the influence of procedural justice on distinct outcomes, with duty to obey affecting legal compliance and normative alignment affecting willingness to cooperate. In sum, most of the causal evidence is congruent with the theory of procedural justice