Pedestrian stops – a form of proactive policing – have been widely used in the US and the UK as a way to prevent crime, but have been criticised as being harmful to those who are stopped. In a new systematic review, David Weisburd, Kevin Petersen and Sydney Fay find that while Stop, Question and Frisk policies reduced crime by about 13 percent, it led to negative mental and physical health problems for those stopped, as well as increased negative perceptions of police and increased self-reported delinquency. Given the harms to individuals stopped by police, they argue that police executives should consider using other less harmful proactive policing strategies.

The use of pedestrian stops, commonly known as SQFs (Stop, Question and Frisk), has been one of the most common yet controversial proactive strategies in modern policing. Given their potential to harm individuals, police executives are faced with the question of whether pedestrian stops should be a part of the toolbox of proactive policing, and if so, how they should be used.

We thought that a first step in answering this policy question would be to objectively review the evidence on SQFs via a Campbell Systematic Review. For studies to be considered eligible for this review, the evaluation was required to include a group that received a pedestrian stops intervention and a separate comparison group that did not receive a pedestrian stops intervention. Our systematic search strategies yielded 40 eligible studies. 

The vast majority of included studies were conducted in the United States, though a handful of studies took place in Europe. Non-US studies generally took place in the United Kingdom (71 percent of non-US studies), and two involved respondents from multiple European countries. Nearly three-quarters of our eligible studies used individuals as the unit of analysis rather than geographic areas. The most common outcomes included crime and disorder, mental and physical health, and attitudes toward the police. 

The effects of police pedestrian stops

The review showed that SQF interventions were associated with a reduction in crime of approximately 13 percent for intervention areas relative to the areas where pedestrian stops did not occur. The results also found a diffusion of crime control benefits, however, these results seem to be driven by one study receiving a large amount of weight in the analysis.

Based on eight studies, individuals stopped by police were associated with a 46 percent increase in the odds of a mental health issue (e.g., anxiety, depression, suicidality). The four studies measuring physical health outcomes (e.g., functional limitations, sleep problems, self-rated poor health) provided similar results. Overall, there was a 36 percent increase in the odds of a physical health issue for stopped groups compared to those who were not stopped.

Based on nine eligible studies we found that individuals who were stopped had significantly more negative attitudes toward the police than those who had not been stopped. Results from the four eligible studies comparing self-reported crime/delinquency for individuals stopped by police to individuals not stopped by police, show there was a significant increase in self-reported crime/delinquency for stopped groups compared to those not stopped.

“Ban stop & frisk” (CC BY-NC-SA 2.0) by Diane_Krauthamer

A key concern is SQF’s particular impact on youth. In our review, youth samples (ages 18 and under) were associated with a 74 percent increase in the odds of a mental health issue for individuals stopped by the police compared to those who were not, while adult samples were associated with only a 32 percent increase. We note that because of the relatively small number of studies for comparison, these results were only marginally statistically significant. 

Stop, Question and Frisk policies can reduce crime but can harm those who are stopped 

Does existing evidence suggest that SQF policies reduce crime? The answer is yes. Our Campbell Systematic Review found a 13 percent reduction in crime as a result of pedestrian stop interventions in the areas examined. In turn, we found no evidence of displacement of crime as a result of pedestrian stops.

Absent other information on potential harms, these findings would ordinarily lead to the conclusion that SQFs are an evidence-based policing strategy, and should be seen as an important part of the tool box of policing. However, there has been much criticism of SQFs for their potential to harm individuals, which leads us to our second question: Are claims of negative impacts on individuals confirmed by research? Our findings support those that have cautioned about the use of SQFs as a routine policing strategy. Based on eight available studies, we find evidence of strong negative health consequences for individuals who are stopped. Similar impacts are found on physical health. We also found that attitudes toward the police were affected negatively by SQFs. And finally, SQFs appear to lead to increased self-reported crime or delinquency.

This leads us to a third question: How should police weigh these costs and benefits? Police executives should at the very least implement SQFs as a proactive policing strategy with significant caution. Crime prevention benefits will not be gained without costs. And those costs may be substantial. Our finding that youths appear to suffer more harm than adults, only reinforces these concerns. One question is whether those harms can be mitigated with better training and supervision of police carrying out SQFs. Unfortunately, there are few studies that can provide direct guidance on this question, and these studies are inconsistent regarding the characteristics of police stops and the outcome measures examined.

Other proactive police strategies may be the answer

Finally, we asked how the impacts of pedestrian stops compare with other proactive policing strategies? Recent reviews on hot spots policing and problem-oriented policing (POP) have reported crime reduction effects that are larger in magnitude than those reported here. It appears from what we know that similar or even larger crime prevention gains as those observed for SQFs can be achieved with proactive policing strategies evidencing fewer risks of harm.

This does not mean that SQFs should not have any role as a proactive policing strategy. It may be the case for example, that places with serious gun violence or violent crime problems may warrant this type of aggressive policing strategy. Here the costs and benefits might alter the equation used to assess pedestrian stops. However, we think based on existing reviews that standard crime problems at crime hot spots or in high crime areas are likely better dealt with by other proactive policing approaches. More research is needed before we can conclude that SQFs will provide enough additional benefit in responding to the most serious violent crime problems to outweigh possible harms. At present, the evidence does not support the widespread use of Stop, Question and Frisk as a proactive policing strategy.

• This article is based on the paper, ‘Does Scientific Evidence Support the Widespread Use of SQFs as a Proactive Policing Strategy?’ in Policing: A Journal of Policy and Practice (Oxford University Press) 
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• Note: This article gives the views of the author, and not the position of USAPP – American Politics and Policy, nor the London School of Economics. 
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