The impact of police numbers on crime rates

While studies have examined the relationship between police officer numbers and crime, they have generally not looked at what the officers were doing at the time. The 'what works' evidence suggests the police could reduce crime simply by spending more time on effective activities, and less time on ineffective activities. (see Targeted approaches to crime and disorder reduction).

Bradford's (2011) review of the literature found there was not enough evidence to conclude that an increase in police officer numbers can cause a reduction in crime. Almost all of the studies included in that review had limitations and were inconclusive. Nevertheless, while no single study pointed to a cause-and-effect relationship, the body of evidence – when taken together – suggested the potential for police officer numbers to be negatively associated with some types of recorded crime. In other words, the studies tentatively indicated that when police numbers were higher, crime was likely to be lower.

The potential association between police numbers and crime was found to be stronger for property and other acquisitive crime. For example, Levitt (1997) estimated that a 10% increase in officers was likely to be associated with a 3% reduction in property crime. The review found that evidence of an association between police numbers and violent crime to be weaker and sometimes contradictory (Bradford, 2011). Officer numbers may also affect how much crime is reported and recorded, regardless of changes in underlying victimisation levels (eg, Vollaard and Hamed, 2012).

Many of the studies included in Bradford's (2011) review provided evidence of the impact of one-off and large-scale changes in police deployment under unique circumstances – usually short, sharp increases or reductions in visible numbers due to police strikes or terrorist attacks. For example, there is evidence that a large-scale and widely advertised temporary reduction in police numbers due to a strike is associated with increased crime (Makinen and Takala, 1980). Conversely, the temporary deployment of a large number of officers following the 7/7 bombings in London was associated with a reduction in crime (Draca and others, 2011). Given that such deployment patterns are short term – and often related to other events – they provide limited evidence about the potential impact of smaller changes in police officer numbers. Indeed, there is some evidence to suggest that marginal changes in officer numbers may not be noticed by the public, and do not result in them rethinking how likely it is they could be arrested (Kleck and Barnes, 2014).

References

Bradford B. (2011). 'Police Numbers and Crime Rates – A Rapid Evidence Review'. London: Her Majesty's Inspectorate of Constabulary.

Draca M, Machin S and Witt R. (2011). 'Panic on the Streets of London: Police, Crime, and the July 2005 Terror Attacks'. American Economic Review, 101(5), pp 2157-2181.

Kleck G and Barnes JC. (2014). 'Do More Police Lead to More Crime Deterrence?' Crime & Delinquency, 60(5), pp 716-738.

Levitt S. (1997). 'Using Electoral Cycles in Police Hiring to Estimate the Effect of Police on Crime'. The American Economic Review, 87(3), pp 270-290.

Makinen T and Hannu T. (1980). 'The 1976 Police Strike in Finland. Scandinavian Studies in Criminology', 7, pp 87-106.

Vollaard B and Hamed J. (2012). 'Why the Police Have an Effect on Violent Crime After All: Evidence from the British Crime Survey'. Journal of Law and Economics, 55(4), pp 901-924.

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