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Causal peer effects in police misconduct


We estimate causal peer effects in police misconduct using data from about 35,000 officers and staff from London’s Metropolitan Police Service for the period 2011–2014. We use instrumental variable techniques and exploit the variation in peer misconduct that results when officers switch peer groups. We find that a 10% increase in prior peer misconduct increases an officer’s later misconduct by 8%. As the police are empowered to enforce the law and protect individual liberties, integrity and fairness in policing are essential for establishing and maintaining legitimacy and public consent1,2,3,4,5. Understanding the antecedents of misconduct will help to develop interventions that reduce misconduct.

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Data availability

The data that support the findings of this study are not publicly available. If you would like to view and reproduce our results, please contact E.G.Q.-T. to organize a supervised visit to our local network.

Code availability

Analyses were conducted in R 3.4.5 and Stata 13.1. All code is available in the public repository https://github.com/edikaQT/misconduct_peer_effects.

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Change history

  • 12 June 2019

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.


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This work was supported by Economic and Social Research Council grants ES/K002201/1, ES/P008976/1, ES/N018192/1 and Leverhulme Trust grant RP2012-V-022. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

Author information

Data were provided by the Metropolitan Police Service to N.S. The concept for the paper was developed jointly by the authors. E.G.Q.-T. designed and completed all the analysis and wrote the manuscript of the paper. Both authors revised the manuscript and approved the final version.

Competing interests

The authors declare no competing interests.

Correspondence to Edika G. Quispe-Torreblanca or Neil Stewart.

Supplementary information

  1. Supplementary Information

    Supplementary Methods, Supplementary Figures 1 and 2, Supplementary Tables 1–13 and Supplementary References.

  2. Reporting Summary

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Fig. 1: The identification strategy for peer effects.
Fig. 2: Fitted probability of misconduct at t conditional on the proportion of peers exhibiting events of misconduct in t − 1.