O n August 31, 2015, the New York Times ( Times ) ran a story with the headline "Murder Rates Rising Sharply in Many U.S. Cities." The Times reported that at least 35 cities had seen increases in violent crime compared to 2014, but the story specifically highlighted increases in reported homicides in 10 cities. According to the Times , homicides have increased 76% in Milwaukee, WI; 60% in St. Louis, MO; 56% in Baltimore, MD; 44% in Washington, DC; 22% in New Orleans, LA; 20% in both Chicago, IL, and Kansas City, MO; 17% in Dallas, TX; 9% in New York City; and 4% in Philadelphia, PA. The Times story followed reports from other media outlets about a growing number of violent crimes in some cities. The recent increases in violent crime have grabbed the attention of law enforcement officials. The Major Cities Chiefs Association held a summit in Washington, DC, in August to discuss why it was increasing in some cities and what could be done to reduce it. The Department of Justice (DOJ) held a meeting on October 7 with officials from 15 cities to discuss how DOJ's resources could be utilized to help combat increases in violent crime. After years of declining crime rates, policymakers might consider legislation to reduce or eliminate some mandatory minimum sentences and reduce the number of people held in prison. The changes policymakers might consider could roll back some of the changes Congress made to criminal justice policy during the 1980s and early 1990s in response to long-term rising crime rates. In general, these changes increased sentences, especially for violent and drug offenses, and ensured that inmates served a greater proportion of their sentences in prisons. However, some observers are now concerned that recent reports of an increasing number of violent crimes, especially homicides, in some cities might stymie criminal justice reform in Congress. There has also been a spate of high-profile police-involved deaths over the past year. This has led to calls for legislation to reform police policies and tactics. Some observers are concerned that reports of rising numbers of violent crimes might thwart efforts to increase police accountability if those efforts are viewed as hampering law enforcement's ability to control crime. Has the United States reached the end of, as one criminologist characterized it, the "great American crime decline?" The general consensus is that it is too early to draw any conclusions about the reversal of long-term trends. Also, there are several explanations for why some cities might be experiencing an increase in violent crime other than that the recent era of diminishing violent crime is coming to a close. Reports of an increasing number of violent crimes in some cities do not necessarily mean that the United States is in the midst of a crime wave. Violent crime and homicide rates have been trending downward for more than two decades ( Figure 1 ). The nation's violent crime rate in 2014 was the lowest it has been since 1970, while the homicide rate was the lowest since 1960. Even if homicide and violent crime rates are on the upswing in 2015, the homicide rate would have to increase by 5.7 homicides per 100,000 people to reach the post-1960 high of 10.2 per 100,000, while the violent crime rate would have to increase by 392.7 violent crimes per 100,000 people to equal the post-1960 high-point of 758.2 per 100,000 in 1991. Both of these increases would represent more than a doubling of the 2014 homicide and violent crime rates. As the figures below indicate, Uniform Crime Report (UCR) data from the Federal Bureau of Investigation (FBI) lags by a year. Data on a rising number of homicides or other violent crimes generally comes either from a law enforcement agency or a state UCR program. Data show that since 1990, homicide and violent crime rates in large and medium-sized cities have mirrored national trends ( Figure 2 and Figure 3 ). All cities with populations of 50,000 or more had lower homicide and violent crime rates in 2014 compared to 1990, with the largest cities (i.e., cities with populations of 250,000 or more) experiencing the greatest decreases between those years. In general, crime data should be viewed over longer time periods in order to determine trends. For example, even though violent crime and homicide rates have been on a downward trend since the early 1990s, there were years where one or both increased, but those year-to-year increases did not portend a break in the overall trend. Evaluating crime data in short intervals (quarterly or monthly, for example) can amplify the "noise" in the data and make it harder to distinguish the underlying trend. There are several factors that might help explain some of the reported upticks in violent crime across the country: Year-to-year changes in crime rates can be subject to random fluctuations and not related to how the police do their job . For example, a short-term but intense dispute between rival gangs might lead to an increase in reported violent crimes. Crime is subject to seasonal effects. It tends to increase in the summer and decrease as the year goes on. So a year with a flood of homicides in July may still end up being roughly in-line with the previous year's total by December. Increases in crime might also be indicative of past successes (i.e., many of the reported increases in homicides are from cities where homicide rates are at historic lows, therefore it is possible that, at some point, homicides rates were going to increase compared to the previous year). Percentage change in reported crimes is a relative measure and is sensitive to magnitude. For example, an increase in 10 homicides in a city with 20 homicides the previous year would represent a 50% increase year-over-year, but an additional 10 homicides in a city with 100 homicides the previous year would only represent a 10% increase. In addition, percentage change can sometimes be misleading depending on the time period chosen. For example, if a city had 20 homicides by the end of March 2014 but recorded 25 homicides by the end of March 2015, that would represent a 25% year-to-year increase in the number of homicides. However, if that gap persisted and the city ended the year with 105 homicides compared to 100 homicides in 2014, it would represent a 5% increase in the number of homicides. Also, it is possible that increases in violent crime in some cities do not portend a nationwide increase. An analysis of homicide data from a broader array of cities than those cited in the Times article provides a more nuanced insight into the issue. Data from the nation's 60 most populous cities show that reported homicides were up 16% overall and up by 20% or more in 26 cities. On the other hand, homicides were down in 20 other cities. The majority of cities (44 of 60) have not seen statistically significant increases in homicides, but the overall increase in homicides is statistically significant. Also, it is not rare for there to be large fluctuations in the reported number of homicides from year to year. For example, 17 of today's 60 most populous cities had statistically significant decreases in the number of reported homicides in 2009, and in 2005 there were 15 cities that had statistically significant increases in the number of homicides. It is probably too early to draw any definitive conclusions about whether the country is experiencing a reversal of decreasing violent crime rates. Even if final crime data show an increase in homicides or violent crime in 2015, if history is any indicator a one-year increase does not necessarily suggest a reversal of the nation's two-plus-decade crime decline. While it might be too early to make any definitive conclusions about whether there has been a reversal of the decades-long decrease in violent crime, several commentators have speculated about why some cities are experiencing spikes in violent crime. This section of the report provides a brief overview of some of the more frequently discussed possibilities. The "Ferguson effect" is one of the more widely discussed, and controversial, explanations for the recent increases in violent crime in some cities. It posits that protests over police-involved shootings and attempts to reform how police use force are to blame for the recent increases in some areas. Specifically, this theory suggests that in the wake of recent high-profile officer-involved deaths , the police have become reluctant to engage in proactive policing, thereby emboldening criminals. Proponents of the "Ferguson effect" cite what is largely anecdotal and correlational evidence to support their claim. For example, it has been argued that the police in some cities have limited their use of proactive policing techniques , leading to more homicides. It was reported that by November 2014, arrests were down one-third in St. Louis city and county after the August 2014 shooting of Michael Brown in Ferguson, MO. By early November, homicides in the city were up 42%. Baltimore recorded 43 homicides in May 2015 after rioting resulting from anger over the death of Freddie Gray while he was in police custody. At the same time, arrests were down 57% compared to the previous year. On the other hand, data show that the increase in homicides in St. Louis started before Michael Brown's shooting, and arrests were down and homicides were increasing in Baltimore before Freddy Gray died. Also, arrests might have decreased for reasons other than police officers believing they could not do their jobs due to public criticism of how they use force. For example, the reduced number of arrests in Baltimore can be attributed to staffing shortages and the implementation of a new patrol strategy that preceded Freddy Gray's death. In addition, one criminologist has argued that efforts to reform police and reign in the most egregious abuses have not prevented police from being effective crime fighters. He points to the New York City Police Department (NYPD) as an example.