Tracking a murder rate is a lot like following the stock market, albeit with opposite hopes for the long-term trajectory. We want the murder rate to trend down and the stock market to trend up. What makes them similar is their volatility or “bounciness” and our visceral reactions to these fluctuations. We fret on days when the markets close sharply down, and we despair on days when there is a spate of killings. Focusing on yearly summaries soothes some of these daily jitters, but even these year-by-year measures can go up and down like a roller coaster. Obsessing too much on even these yearly changes obscures the more important long-term trend. Taking stock as an example, even though the Dow Jones industrial average went down between January 2014 and January 2015, a look at a longer period of time reveals a remarkably robust bull market lasting almost a decade.
So goes the New Orleans murder rate. A news article in The Advocate last New Year’s Eve noted that “homicides climbed by 7 percent to 176 as of noon Saturday, marking the second annual increase in a row.” Back-to-back yearly increases are not what anyone wants to see in the murder rate, but does this really mean that things are getting worse? Or, more to the point, do the back-to-back yearly increases warrant an entirely new approach to violent crime, as some of our mayoral candidates are suggesting? Not necessarily. Because the city’s murder rate is so bouncy, it takes a period of several years to discern whether things are improving or deteriorating, and to decide whether 1) we’re likely to be on the right track with regard to our approach or 2) a major change is warranted.
New Orleans police are seeking a 34-year-old man after a shooting in St. Claude on Tuesday, …
When we run the numbers on New Orleans murder figures over the past decade (2006–2016), we come up with two main findings. First, the city’s murder rate has been going down over the past decade, not up, and down to a substantial degree. The probability that this finding (that the murder rate is going down) is false (in other words, that the murder rate is actually not going down) is about one in a thousand. Second, the most recent part of this most recent decade looks especially promising. Comparing the two most recent four-year periods, we’ve improved from a level of about 50 murders per 100,000 residents to a substantially lower level of about 40 murders per 100,000. This result is also statistically significant, with a probability of being false of less than one in a thousand (we still have three months to go in 2017, but we’re on track for a murder rate of around 40 this year, too). You can see these two results clearly in the accompanying graph if you can avoid being made woozy by the roller coaster.
And you can see the implications of these two results if you can avoid being made woozy by the political rhetoric of the mayoral race. At around the time, the murder rate in New Orleans began its descent from around 50 to around 40, the Landrieu administration implemented a set of anti-violence programs under an umbrella they call “NOLA for Life.” The timing of these two events certainly does not prove cause and effect, just as the smell of coffee does not prove the existence of actual coffee. But the smell is generally compelling enough to draw us into the kitchen. Three years ago one of us thought something might be brewing with the initial correspondence between a drop in the murder rate and the implementation of NOLA for Life, but the results of the data analysis were only suggestive of a downward trend in the murder rate. Now, three years later, the downward trend is clear.
We’re moving in a good direction with regard to the city’s murder rate. Rather than calling for an about-face in fighting violent crime, we would be much better suited if our next mayor built upon the successes of the outgoing administration and led us forward to an even lower level of murder in our city, ever further down towards the lower line near the bottom of the figure, where we belong.