The murder rate went up in 2015. It’s still half of what it was 25 years ago.

After reaching the lowest rate in decades in 2014, America’s murder rate in 2015 went up by a little more than 11 percent.

The increase, reported in the FBI’s latest version of its Uniform Crime Reports, is quite large. It also seemed to hit every part of the country — the rate went up in big to small cities, nonmetropolitan counties, suburban areas, and every major region in the US.

Still, the increase leaves the murder rate below the levels of 2009 and half of where it was in 1991. And other crimes didn’t see nearly as pronounced of changes: The violent crime rate went up by 3 percent (to 372.6 per 100,000 people, which is still below 2012’s levels), rape by 4 percent, aggravated assault by 4 percent, and robbery by less than 1 percent. And burglary and larceny rates actually dropped — with property crime rates falling to levels lower than any point after 1966.

But with an election underway and much of national attention going to the Black Lives Matter movement’s protests of racial disparities in the criminal justice system, the rise in the murder rate has become a hot-button issue.

Some pundits, particularly conservative Heather Mac Donald, argue that what’s taking place is the so-called “Ferguson effect”: the idea that the Black Lives Matter movement’s protests of police — which began in Ferguson, Missouri, after the August 2014 police shooting of Michael Brown — have scared police officers from proactively policing and also emboldened criminals, leading to more crime in the US.

Others, especially a long line of criminologists, say there’s need for caution here: There are regular fluctuations in crime data, and as alarming as the increase is in some cities in 2015, we simply don’t know if the trend up will hold for years to come. (Besides, the murder rate is still near historic lows — after all, this is an 11 percent increase from a record low in 2014.)

So what exactly caused the increase? With the caveat that the research on this is very early and we don’t know anything for certain, there are several possibilities — two of which involve the Ferguson effect.

One theory: The Ferguson effect caused the increase in murders

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There are essentially two versions of the theory of the Ferguson effect.

The most well-known version, popularized by Mac Donald, is that Black Lives Matter protests have led police officers to avoid proactive policing — out of fear that a confrontation with a suspect could turn deadly, making the officer the subject of high-profile protests over a police shooting. At the same time, the theory goes, the protests have emboldened criminals, since they’re aware that police are acting less aggressively.

The case for this comes mainly from Baltimore: In 2015, after Freddie Gray died while in police custody, locals protested and rioted. At the same time, the number of arrests in Baltimore dramatically dropped and the local crime rate rose tremendously. The city ended 2015 with a nearly 56 percent increase in its murder rate — an enormous spike.

Mac Donald has argued that the drop in arrests and rise in murders are connected, as she told me earlier this year:

Officers say they are reluctant to engage in proactive policing. That testimony is backed up by data on officer activity where such data exists and is publicly available — such as in Los Angeles and Baltimore, where arrests just plummeted after the Freddie Gray case.

Police chiefs and law enforcement officials testify to the significance of the crime increase and to the likely or possible reason for it, which is the reluctance of officers to engage in discretionary enforcement.

But the FBI data complicates this theory. For one, arrest rates for murders rose by 6 percent from 2014 to 2015, from 3.3 per 100,000 people to 3.5 — not enough to match the 11 percent murder increase, but still an increase. And overall arrest rates decreased by just 4 percent — from 3,512.7 to 3,363.0. If police officers pulling back explained the rise in murders, you would expect to see much larger decreases in the number of arrests — but you don’t.

Another problem: Mac Donald and other proponents of her version of the Ferguson effect have long characterized this as a largely urban problem — it’s midsize and bigger cities that would have the biggest spikes in violence, because these are the places most likely to have large black populations that are protesting the police.

Yet the FBI data shows that the murder increase hit practically every type of city and town in America. Cities with populations of 250,000 or more saw a 14.5 percent increase in the number of murders, with large cities of 1 million and more experiencing a 10.6 percent increase and midsize cities of 500,000 to 999,999 seeing the largest spike, at 20.2 percent. Yet small cities of 10,000 to 24,999 also saw a large increase of 14.1 percent, and nonmetropolitan counties saw a spike of 15.2 percent.

(One caveat: About half of murders still happened in cities with 250,000 people or higher — so the smaller places’ data is likely statistically noisier and more susceptible to small changes.)

Given that nonmetropolitan areas did not see the kinds of Black Lives Matter protests that New York City, Baltimore, St. Louis, and other big cities saw, maybe something else is going on other than the Ferguson effect. But it’s also possible police departments in nonmetro areas also felt some sort of chilling effect from what they saw on the news.

But even if that’s the case, there’s also a question as to why murders saw especially high increases while other types of crime didn’t — and property crime rates in fact dropped. If criminals are emboldened, surely they would be committing all types of crime much more often, not just murder.

Another theory: the flip side of the Ferguson effect

There’s another Ferguson effect theory: It’s not that police were scared and criminals were emboldened by Black Lives Matter protests. Instead, the protests exposed and elevated longstanding concerns about police in America, fostering further distrust in the police. And that loss of trust and faith made it harder for police to do their jobs, leading to more crime.

Richard Rosenfeld, a criminologist at the University of Missouri St. Louis who’s done the most thorough research on the 2015 rise in murders so far, previously told me this interpretation of the Ferguson effect theory likely has the most merit. He studied the murder increase for the US Department of Justice, ruling out other possibilities — that a drop in incarceration and the opioid epidemic caused more violent crime — but said the Ferguson effect merits more research before it’s ruled out.

Rosenfeld argued:

I do find it somewhat hard to believe that the entire increase could be explained simply by the withdrawal of the police. That assumes that the police have an enormously powerful influence on crime rates. And while the research shows that police do influence crime rates — in particular, police actions [known as] “proactive policing” can reduce crime — it's limited. …

There is good sociological and historical evidence that if people lose confidence in the police to protect them, or if they lack trust in the police because they believe the police are harassing them or behaving unfairly, they do tend to take matters into their own hands. So one tends to see preemptive killings and retaliatory shootings go up.

The distinction matters for policy. If Mac Donald’s version of the Ferguson effect is right, then it vindicates aggressive policing tactics — it suggests that police need to be willing to act aggressively on the job to deter crime. If the other version is right, it suggests aggressive policing tactics caused more crime — they led to widespread distrust in the police, and the research shows that diminished trust in the police can cause more crime as people are compelled to deal with interpersonal disputes outside the law.

Still, the other Ferguson effect theory runs into the same problems as Mac Donald’s version: If the issue is lack of trust in the police, particularly in big cities where Black Lives Matter has been so active, why is one of the biggest murder rate increases in nonmetropolitan areas? If people are dealing with their own issues outside the law, why did murder arrest rates increase? And why did rates for other types of crime not increase as much — or at all, in the case of property crimes — compared to murder?

What else could explain the murder increase?

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If it isn’t the Ferguson effect (and, again, we don’t know that yet), what is going on?

The other possibility, echoed by every criminologist I’ve talked to about this, is that this is a short-term fluctuation in the data that doesn’t show a longer-term trend. The murder rate is generally low, so it’s very prone to big statistical fluctuations without much explanation if one year just happens to be a bit worse than the previous one. We saw this in 2005 and 2006: The murder rate went up from 5.5 per 100,000 people in 2004 to 5.6 in 2005 and 5.8 in 2006 — before dropping all the way down to 4.4 in 2014.

The same thing could have happened in 2015. For whatever reason, maybe even some version of the Ferguson effect, 2015 was just a particularly bad year for murders. But maybe (hopefully) it was just a blip in the data and the long-term trend will continue to go down.

Another possibility is that something else happened in 2015 that we just don’t know about. Consider: Criminologists are still debating what caused the massive drop in the violent crime and murder rates over the past couple of decades — a roughly 50 percent decrease since the 1980s and ’90s. There are many theories, from changes in policing tactics to more incarceration to reductions in lead exposure, but no one knows for certain what the definitive cause was. Given that people have had more time to study the big crime drop and less time to study the 2015 murder spike, maybe there’s something out there causing more crime and murders that we just don’t know about yet.

Statistical fluctuations and “we don’t know” aren’t the most satisfying answers. But given that they’re seriously plausible possibilities, everyone should probably wait a while longer — maybe even a few years — before trying to build a definitive theory around one year of bad crime statistics.

As alarming as the increase is, the data is already really old

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You may have noticed that we are three-fourths done with 2016 and we’re just now talking about the full 2015 crime data. To many criminologists, this is a huge problem in how the US reports its crime data.

Rosenfeld told me:

Our crime monitoring system — if that's what one wants to call it — is based on the Uniform Crime Reports from the FBI. It is woefully inadequate, and it need not be. I've been calling for a long, long time for a Uniform Crime Reports program to release monthly crime statistics in a very timely way.

So we should be seeing crime data, at least for the large cities in the United States, one or two months after the month the data was collected — just as we do for unemployment; just as we do for inflation; just as we do when influenza breaks out, and the CDC is able to give us weekly case counts.

As Rosenfeld suggested, it doesn’t have to be this way. City and state police agencies are already collecting crime data. They are just slow to report it, and the FBI is slow to compile it.

This, too, has policy implications: If the murder rate is going up, it would be helpful for lawmakers and police to know about an increase much sooner — preferably as it’s happening — and be able to judge whether the trends are local, statewide, or national to find the right solutions. Yet it took until late 2016 to finally conclude that violent crime and murder rates really did go up nationwide in 2015.

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