In the last few weeks, shootings and violent incidents have made headlines every day.

Another summer means another spike in violence across Philadelphia.

We've been here before. You may recall that after a particularly devastating summer in 2007, Mayor Michael Nutter declared a "crime emergency" and brought in Commissioner Charles Ramsey to reduce violence by the following summer.

Since then, violent crime has reduced substantially in Philadelphia, though with a worrying increase in the last few years. Even when crime was on the decline, we still experienced summer spikes.

According to data pulled from OpenDataPhilly, the city's online data depository, total crime incidents have increased in the summer months and dipped during winter months from 2006 through 2018.

Staff Graphic

My colleagues Ralph Taylor and Evan Sorg have shown that for every 10-degree increase in temperature, Philadelphia's street robberies increase by about 2 percent. This effect is especially pronounced in places with more commercial land use and near subway stations.

Possible causes

Why does this happen? One of the most likely causes is due to what is called routine activities theory.

More of an established scientific maxim than a "theory," we know that for crime to occur, a likely offender has to interact with a suitable target in a place with low levels of guardianship. The National Academies of Sciences has recognized routine activities theory as a foundation for why crime prevention focused at high-crime places has been successful.

In the depths of winter people stay in the warmth — and relative security — of their homes. But with good weather, people spend more time outside, interacting with neighbors and socializing in public places. Increasing our time outside heightens our chances of being either a victim or a perpetrator of violence.

It can concentrate in our poorest neighborhoods where people can't afford to retreat to air-conditioning.

And the combination of more daylight and no school increases the risks for children.

When you also consider the hot humid weather can make some people more aggressive and short-tempered, and drink more, the spike in violence becomes sadly understandable.

How to make summers safer

How then to limit the harm? One way is to move away from doing things that feel good, toward things that do good.

This demands a more evidence-based approach to the city's violence reduction strategy. I'm not talking about forensic evidence, but rather scientific confirmation that a program is actually reducing crime and producing more than anecdotal feel-good stories. As I write in a new book published this month, "Science and research can distinguish between good intentions and good programs."

Philadelphia police investigate a shooting along N. Broad St. just south of Dauphin St. on Monday, August 13, 2012.
ALEJANDRO A. ALVAREZ / STAFF PHOTOGRAPHER
Philadelphia police investigate a shooting along N. Broad St. just south of Dauphin St. on Monday, August 13, 2012.

The city's crime control policy can be more evidence-based in a couple of ways.

First, we can choose strategies that have been demonstrated to work. Funding these will mean curtailing programs that are not performing. For example, the city promotes paid summer jobs for young people as a resource for violence reduction; however, researchers have known for 20 years that summer jobs programs do not have any crime prevention effect. And while gun buy-back programs may help police-community relationships, the research evidence is clear that they don't reduce violence.

Why not, then, do less, with more? This means providing more resources for a narrower range of programs that have been shown to be effective. For example, two major Philadelphia police projects demonstrated that both uniformed cops on street-corner foot beats, and the specific targeting of serious, violent offenders, could reduce violent crime. Concentrating police in crime hot spots makes sense because the risk is not shared equally across our city. In the Northeast the homicide risk is on a par with residing in tranquil New Zealand, while North Philadelphia is like living in El Salvador. The Philadelphia Police Department has been a pioneer of hot-spots policing in the past, and continues to do so, though it is easy to dilute the benefits.

Since Ramsey's time, the foot beats have grown in size considerably, given the understandable desire to extend this crime-reduction and community-engagement approach to as many communities as possible. They are, however, most effective when focused on smaller, concentrated high-crime hot spots. And the current gun-violence reduction task force would benefit from more resources to support their offender targeting, given the evidence that supports the benefits of focusing on the worst of the worst.

Another program that has shown promise with real results is Focused Deterrence. Focused deterrence strategies target small groups of high-risk offenders with the threat of enhanced law enforcement and prosecution blended with community mobilization and the offer of social service support. They require considerable effort and collaboration but can reap meaningful rewards. When it was run in South Philadelphia, shootings decreased by 35 percent. Considering we spend over $45 million on violence prevention, it is disgraceful that a program that has strong empirical evaluations behind it garners a measly $130,000.

A further way we can employ a more scientific approach is to evaluate current and new programs. Citizens have a right to expect that their taxes are spent judiciously, but as columnist Helen Ubiñas has recently highlighted, we spend over 13 million city dollars on programs that claim to reduce violence, yet we have little evidence that they have a scrap of benefit. Mandating rigorous evaluation as a requirement of antiviolence projects that exceed a certain cost would increase transparency and help us learn what works and when.

Smart policing and evidence-based crime prevention can go only so far. They won't eradicate the underlying economic disparities, opioid challenges, or structural difficulties of a city awash with handguns that can fuel so much of the city's woes. And they must be conducted in a fair, constitutional, and respectful manner. But we can work smarter to enhance the benefits of programs that are shown to work, reduce spending on strategies that don't, and use Philadelphians' tax dollars in the most evidence-based way possible.

Jerry Ratcliffe is a professor of criminal justice at Temple University. This month he publishes a new book, "Reducing Crime: A Companion for Police Leaders." @jerry_ratcliffe