Over the past few months, media outlets have warned about a supposed nationwide crime wave. The New York Times published a front-page story that claimed "murder rates [are] rising sharply in many US cities." CNN, USA Today, and NPR ran similar stories.

An analysis from the Brennan Center for Justice, published in November and updated on Monday, pushes back against these claims, presenting a more mixed picture.

The report shows some cities are expected to see a dramatic increase in murders in 2015 compared with 2014 — Baltimore's murder count, for example, is projected to go up by 62.8 percent this year. Overall, the average murder rate will climb by 14.6 percent in 25 of the nation's 30 largest cities — a very big increase.

But the report finds some big cities have seen decreases — Boston, for one, is expected to have a 25 percent drop in murders. And the increases in murders don't necessarily translate to overall rises in crime — despite the general escalation in murders, overall crime is expected to fall by 5.5 percent in 19 major US cities analyzed in the report. So the picture is more mixed than claims of a nationwide crime wave suggest.

For the analysis, the Brennan Center requested murder and crime statistics from the 30 most populous US cities, getting responses from 25 localities for murders and 19 for overall crime. It then compiled the data in an analysis that gives a much broader picture than the more limited data analyzed and published by media outlets.

The report disputes the idea that there's a nationwide increase in crime. But more than that, it pushes against the broader narrative that criticisms of police use of force over the past year — driven by the Black Lives Matter movement — are demoralizing police officers and emboldening criminals, leading to more crime. After all, if a nationwide movement really were leading to more crime, one would expect to see it in the numbers. But the data, in fact, shows a messier picture — one that may warrant more caution before reaching sweeping conclusions.

Murders are up in many big cities

As the chart above shows, most of the 25 big cities looked at by Brennan saw increases in the number of murders. Among the cities that provided data, Brennan found 18 are projected to see increases in the number of murders in 2015 compared to 2014, while one city is projected to see no change and six are expected to see decreases.

But the Brennan report cautioned against making too much of the projected rise in homicides:

[I]n absolute terms, murder rates are so low that a small numerical increase leads to a large percentage change. Even with the 2015 increase, murder rates are roughly the same as they were in 2012. Since murder rates vary widely from year to year, one year’s increase is not evidence of a coming wave of violent crime.

The report also argued that a bulk of the increase — in Baltimore and Washington, DC, in particular — appeared to be a result of local factors:

Just two cities, Baltimore and Washington, D.C., account for almost 50 percent of the national increase in murders. These serious increases seem to be localized, rather than part of a national pandemic, suggesting community conditions are a major factor. The preliminary report examined five cities with particularly high murder rates — Baltimore, Detroit, Milwaukee, New Orleans, and St. Louis — and found these cities also had significantly lower incomes, higher poverty rates, higher unemployment, and falling populations than the national average.

But crime is down in 11 of 19 major US cities

When looking at overall crime rates, the trend looks a lot more positive. There aren't huge spikes in crime rates in any of the 19 cities that provided data to Brennan. And 11 cities reported decreases, including some of the cities that reported increases in the total number of murders.

Brennan notes that this is part of a much broader crime drop in the past few decades: "The crime rate is now half of what it was in 1990, and almost a quarter (22 percent) less than it was at the turn of the century."

The count is based on the FBI's "index crimes," so it includes figures for murder, non-negligent manslaughter, robbery, larceny (theft), aggravated assault, burglary, and motor vehicle theft.

You also may notice that the change in these numbers is smaller overall. That's because the crime rate measures many more variables — with murder just one factor among many — so it's less susceptible to the kinds of swings seen in the murder numbers. That's one reason Brennan prefers using the overall crime data over the murder numbers to see what's going on in US cities — the crime data is less noisy.

The report pushes against the "Ferguson effect"

Over the past year, there's been a lot of talk about what some critics have called the "Ferguson effect": the idea that more scrutiny of police since the Ferguson, Missouri, protests has demoralized cops and emboldened criminals, leading to more crime in major US cities. Both FBI Director James Comey and DEA chief Chuck Rosenberg have said the idea has some credence, based on what they have heard from police chiefs and officers around the country.

But many criminologists have pushed back against the claim, arguing that annual crime and murder data is generally noisy and constantly fluctuating, and that it's too early to reach any big conclusions. They point out, for instance, that some of the crime increases that proponents of the Ferguson effect have pointed to — in St. Louis, for example — started before protests in Ferguson. "The people who point to the Ferguson effect as the reason for the increase haven't been consulting calendars very carefully," Franklin Zimring, a criminologist at the University of California Berkeley, told me in September.

The Brennan report casts further doubt on the claim of a Ferguson effect. If a nationwide protest movement like Black Lives Matter really were leading to more crime and murders, one would expect to see the effects on a national level. But Brennan's findings are more mixed: Some big cities are seeing increases in murders in 2015, others aren't, and several major cities with increases in murders are seeing drops in overall crime. And the general crime and murder figures are still much lower than they were just a few decades and even years ago.

At the very least, the messy picture demonstrates that there is a lot going on in these numbers, and perhaps it's better to wait to see and study the full nationwide crime numbers for 2015 — which the FBI will release next year — before reaching any sweeping conclusions about where the country is headed and why.

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