Micro Places – Ariel et al. (2020)

Study Reference:

Ariel, B., Sherman, L. W., & Newton, M. (2020). Testing hot-spots police patrols against no-treatment controls: temporal and spatial deterrence effects in the London underground experiment. Criminology, 58(1), 101-128.

Location in the Matrix and Methodological Rigor:

Micro places; General; Proactive; Very Rigorous; Effective

What police practice or strategy was examined?

This study evaluated the effects of directed foot patrols targeted at hotspot platforms in the London Underground over a 6-month period from late 2011 to early 2012. The intervention involved two-person patrol units engaging in 15-minute patrols during high crime hours and days (i.e., Wednesdays through Saturdays from 3 pm – 10 pm).  Patrol units were assigned three to five hotspot platforms to patrol during the study and asked to visit these hotspots in a random order (4 times per day) to increase the uncertainty of police presence. During their foot patrols, officers were instructed to remain visible on the platform and engage with the public, but were not tasked with any problem-solving, community policing, or other targeted initiatives. After each patrol, treatment officers moved between hot spots by train. Monthly “motivational debriefs” were also held to provide feedback to patrol officers about crime figures and to keep officers motivated on the intervention.

How was the intervention evaluated?

A randomized experiment was conducted to evaluate the intervention. London Underground’s platforms were ranked based on the level of crime during a twelve-month period. One hundred fifteen hot spots were selected and 57 were randomly assigned to the treatment group while 58 were randomly assigned to the control group. This study used a no-treatment control group, meaning that police were introduced into treatment areas that previously had not been patrolled. The control group, therefore, did not receive any patrol dosage during the experiment. Calls for service and reported crimes within the selected areas were examined for six months pre- and post-experiment. Spatial and temporal displacement outcomes were also tested by examining crimes and calls for service in non-platform areas and on non-patrol days/times.

What were the key findings?

There were significantly fewer calls for service made in the treatment platforms compared to control platforms during the experimental period. There was also evidence of a diffusion of crime control benefits, as calls for service were significantly lower in treatment areas during non-patrol days/times (and in areas surrounding treatment platforms), relative to the control group. Reported crimes also decreased across all outcomes for treatment areas relative to control areas, however, these effects were generally nonsignificant. The authors note that the effect of the intervention on calls for service during patrol days/times is the largest recorded effect in a published experimental evaluation of hot spots policing, however, the largest deterrent effect associated with the intervention occurred in areas surrounding treatment platforms during patrol days/times. Overall, the police prevented more crime when they were absent from treatment areas than when they were present.

What were the implications for law enforcement?

The authors suggest that the effectiveness of hotspot policing has been underestimated by previous research where control areas received nontrivial levels of patrol dosage. By using a no-treatment control group, the authors argue that the deterrent effects of hot spots patrols are larger than previously estimated, and that the level of patrol dosage in control areas is a critical component. Additionally, the authors suggest that police patrols may provide the greatest crime reduction benefit when they are not present, an implication they refer to as the “London Underground Paradox.”

Where can I find more information about this intervention, similar types of intervention, or related studies?