Recent news stories from Chicago have celebrated a dramatic decline in homicides after a terrible 2012. Sixteen homicides were committed in March, compared with 53 in March of last year, an enormous 70 percent difference. The first three months of 2013 saw 67 homicides in Chicago, compared with 122 during the same period in 2012. The tone of news coverage was hopeful—has Chicago turned a corner on its homicide problem?
Homicide is a terrible problem in Chicago, and it’s right and important that we pay close attention to it. But doing so can easily lead to the over-interpretation of monthly and quarterly fluctuations in the homicide rate. Homicide numbers vary considerably over short periods of time, as evident by Chicago’s homicides since 2009 (chart 1).
This variation can be random or can stem from unpredictable factors, such as weather. Warmer weather is usually associated with more crime, and March 2012 was unseasonably warm, with an average daily high temperature of 63 degrees and nine straight days of record highs in the 80s. The average high in March 2013 was 40 degrees.
Media coverage overly focused on the most recent numbers can cause confusion over what constitutes a departure from the norm. Looking at the Chicago homicide figures for recent years, the first quarter of 2012 stands out as being an awful outlier, much deadlier than the start of any recent year. The rest of 2012 was not very different than the previous three years. Viewed from this perspective, the homicide numbers for early 2013 may represent a merciful return to the norm.
This is not to say that the low number of homicides to date in 2013 is meaningless. While benchmarking the figures against the same months in 2012 may overstate how much things have changed, Chicago experienced fewer than 20 homicides in both February and March of this year. Prior to that, the last time there were fewer than 20 was February 2008.
Chicago has invested significant resources in analyzing the drivers of violence, particularly around gang conflicts, and has initiated a variety of anti-violence strategies. Recent signs make us hopeful that these efforts are bearing fruit, but that must be assessed over a longer time horizon than a month or a quarter. Chicago PD Chief Garry McCarthy has been making this point consistently over the past year through bad months with high homicide numbers and in better months, when the trend looks more positive. We would do well to listen.