Policing to protect the population

Law enforcement training often does not rely on the best scientific evidence, and there is much disagreement about what the best strategies and tactics are. In 2021, the National Academies of Sciences, Engineering, and Medicine (NASEM) convened a working group to assess the scientific evidence on police training. The main questions the committee sought to answer were: 1) What are the core knowledge and skills needed for police to promote the rule of law and protect the population?; and 2) What is known about mechanisms (e.g., basic and continuing education or other capacity building programs) for developing these core skills? The answers to these questions were recently published and are discussed below. 

The conference discussions were guided by evidence captured in the Global Police Database, which collates high quality research studies of police-related interventions from 87 countries. Two prior NASEM reports were also used to inform the discussion: Fairness and Effectiveness in Policing: The Evidence (2004) and Proactive Policing: Effects on Crime and Communities (2018). 

Effective Policing Strategies

Empirical facts and well-accepted theories from research can provide knowledge to help police officers make more informed decisions about crime, offenders, and victims. There is also a fair degree of scientific consensus in the research on some policing approaches that can reduce crime and improve police-citizen relationships. 

First, research shows that crime concentrates in a small fraction of all places, as well as certain times of day and days of the week. Data-driven tactics and analysis of crime patterns can be used to identify micro-geographical locations with high concentrations of crime (i.e., “hot spots”) as well as the days and times of week that they are most likely to occur. Using this information, police can then proactively target certain hot spots during specific hours or days of the week that crime is expected to occur. This approach is referred to as “hot spots” policing, and it has been found to be effective in reducing crime across numerous studies, particularly when officers target the specific micro-geographical locations of crime rather than the communities surrounding them. Similarly, police can increase their presence during certain hours or days of the week when crime is expected to peak. Thankfully, the research also has not found evidence of crime displacement, so it is likely that crime reduction benefits are real and not just shifted to a new location. 

Hots spots strategies likely work because they increase the risk of apprehension for would-be offenders, which in theory deters criminal behavior. In addition, police presence disrupts the routine activities of an area, which can decrease the potential convergence between a motivated offender and a vulnerable target. Further, research has found no evidence of displacement, suggesting that the strategy is effective in reducing crime without pushing it elsewhere. However, hot spots strategies that emphasize more community engagement rather than crime control are less likely to result in crime reduction effects, though they do seem to improve citizen satisfaction and perceptions of the police. 

Second, we know that crime concentrates among a small percentage of offenders. If police can successfully identify and target these offenders, it can reduce crime. To identify prolific offenders, officers can gather intelligence to learn more about an individual, their frequent activities and favorite locations, and the people they interact with. These approaches can also be informed by geographical analysis, but tend to rely more on other types of intelligence information specific to the offender. The rule that a few high-profile offenders cause the most harm is also true in terms of domestic violence. In this case, selectively targeting the highest risk individuals is also a helpful strategy, though it takes a slightly different approach that relies less on social network analysis and more on the offender’s prior history. 

Focused deterrence approaches (commonly known as “Operation Ceasefire” or “the pulling levers approach”) are typically used to target high-risk offenders, gangs, and those involved in illegal drug markets. These programs reach out directly to individuals at high risk of committing serious violence in the future to communicate the threat of sanctions, the promise of surveillance, and the support of resources that can help integrate individuals back into law-abiding society and behavior. Numerous studies on focused deterrence programs have found moderate reduction in serious crimes. Not surprisingly though, the effectiveness of focused deterrence depends largely on whether the right offenders are being targeted and whether offenders are actually participating in the program.

When it comes to domestic violence, selective targeting of the most dangerous domestic violence offenders can be done through lethality assessments and protection orders. Lethality assessments can be used by law enforcement to assess an individual’s risk of future intimate partner homicide. Lethality assessments rely on information from a perpetrator’s history and prior behavior (for example, prior suicidal behavior and past strangulation attempts) to predict future dangerousness. This information can be used to monitor protection orders and ideally prevent intimate partner homicide. When it comes to protection orders, research has found them to be effective in reducing severe domestic violence re-victimization, but less effective in cases with non-severe and non-physical forms of re-victimization.  Police training should ensure that officers have the skills to administer validated risk assessments when protection orders are processed to help police better monitor selective offenders. 

For these approaches to be effective, the experts also agreed that several skills are needed to facilitate translating this knowledge into effective policing strategies and tactics. These skills include: 1) the ability to effectively interact with the public in a professional and respectful manner; 2) critical thinking skills to apply and synthesize theoretical or evaluation knowledge into the real world; 3) data skills to understand, measure, and analyze crime data to inform decision-making; and 4) skills to work with local and governmental partners in providing integrated services, such as focused deterrence.

Training Delivery Methods

There are also different ways to deliver police training. Most police recruits in the United States will receive an average of six months of basic academy training followed by approximately four months of experiential learning within a field-training setting. Sometimes, field training is followed by a final block of learning within an academy setting, but this is less common. After an officer begins serving full-time, they will often receive in-service training at somewhat regular intervals throughout the duration of their career. In-service training can take place in a variety of settings that might be formal or informal. For example, formal in-service training might require an officer to return to an academy setting for a few hours or days to obtain certain specializations (e.g., firearms), whereas informal training might occur during daily roll calls or at other times during an officer’s shift.

A variety of teaching methods have been used for in-service training (e.g., lecture/classroom-based, web-based, simulations, role-play scenarios, supervisory meetings), but the approach to in-service training varies even more than recruit training. First, the frequency and dosage of additional in-service and specialized training varies, and in some agencies, specialized training may only be available to a privileged few. Finally, police officers and other police supervisors and commanders may attend specialized in-service training programs that are not offered to everyone.

But the evaluation on these types of programs is largely absent, and popularly promoted and frequently used training programs (e.g., de-escalation, procedural justice, implicit bias training, and community-oriented policing) remain under-evaluated. Much of what is known about training design comes from other work contexts, particularly from health care settings. Nonetheless, best practice for delivery suggest that long-term learning is best accomplished by repeated experience of critical tasks and skills distributed over multiple training sessions, instead of relying on one-time training programs. Some research also suggests that the trustworthiness of organizational leadership and instructors can influence training outcomes.

Overall, we don’t know much about different training content or methods used for training delivery in police departments, and most of the reason for this is poor documentation. In particular, it is very rare for police departments to measure outcomes and track success over time, and it is also unlikely that they will thoroughly document information related to training implementation and the quality and nature of training across different instructors or modalities. It is critical that departments track this information and assess outcome measures to determine whether the training is achieving desired goals. Training methods should include an evaluation component whenever possible, ideally one with a credible causal design. Perhaps, more police departments can consider partnering with a nearby university or researcher to help them evaluate the efficacy of their programs.


Training is often not aligned with evidence-based tactics. However, there is scientific consensus on several police strategies that have been shown effectiveness in prior research.

First, crime concentrates among very specific micro-geographical places, at specific times and days of the week. Crime also concentrates among a small number of prolific offenders.  Crime also tends to concentrate among repeat victims, particularly in the case of family violence. 

There are some interventions have been tested with proven effects that have achieved a fair degree of scientific consensus regarding their efficacy. One of these is hot spots policing, which involves the use of data to geographically target crime. Hot spots is a place-based intervention, but it can also be applied in a specific fashion to target certain times and days of the week.

Focused deterrence is an approach that selectively targets prolific offenders and deters them from future criminal behavior through threat of formal sanctions from various angles. Geographical analysis can inform this approach if it shows where offenders tend to hang out, but it is not always needed. When it comes to domestic violence perpetrators, the use of lethality assessments is often helpful in predicting future dangerousness and monitoring protection orders. 

At present, there is a solid foundation of evidence supporting the effectiveness of a few different police strategies, but little is known about the underlying trainings that support these strategies. When it comes to training, more work is needed to understand the best way to deliver training for maximum effectiveness. 

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