Research Press Release

Society: Militarization of police may not reduce crime in the US

Nature Human Behaviour

December 8, 2020

Studies that have been used to justify the provision of surplus military equipment to local police in the United States may be based on unreliable data, suggest two separate papers published in Nature Human Behaviour. More recent data also indicate that such militarization might not reduce violent crime.

In the United States, the transfer of surplus military equipment (SME)—including vehicles, weapons and attire traditionally associated with combat—from the Department of Defense to police departments and sheriff’s offices contributes to the militarization of local law enforcement. Many in the US are concerned about how this shift in policing affects public safety. Proponents view SME as lifesaving and critical to fighting violent crime. Opponents say that the equipment is to blame for excessive force by police and that its acquisition is motivated by racial threat.

In 2017, the Trump Administration reversed Obama-era restrictions of militarization, citing two studies that reported that SME reduces crime rates and assaults against police officers. Tom Clark and colleagues examined the robustness of the claims presented in these two papers. The studies were based on government SME records, made available to the public in 2014. The authors found significant discrepancies in the data about which law enforcement agencies have and use SME. For example, there were missing items, such as firearms, that were shipped, but not recorded as being received by the relevant agency, and some counties reported no SME transfers, even though records indicate that they received equipment.

The authors conclude that drawing firm conclusions and promoting claims about the positive policy efficacy of police militarization—especially for crime rates—based on papers relying on the SME data released in 2014 is unreliable. When they conducted a new analysis using updated data, the authors found no evidence that SME transfers reduce crime.

In a separate paper, Kenneth Lowande also examined the substantial limitations of data used to analyse the effects of transferring SME to law enforcement. He used 3.8 million archived inventory records to estimate the magnitude of sources of bias in existing studies SME transfers. He found the most variation in data from previously unobserved sources: in one 3-month period, more than 15,000 controlled items vanished from agency inventories and more than 4,000 were received for transfer. This implies that studies purporting to show crime-reduction benefit are unreliable. Lowande then compared the 2014 data to data collected when the Obama administration recalled SME in 2015, which resulted in the forced demilitarization of several hundred departments. Proponents of SME transfers say that demilitarization would lead to an increase in violent crime, but Lowande found little-to-no evidence that demilitarization had an impact on violent crime or officer safety.


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