We got a letter and a chart this weekend from Dr. A. Charles Catania, a behavior analyst and experimental psychologist with the University of Maryland, Baltimore County. He had been looking at a report on the deadliest shootings in the American history. Catania wrote:
When the Washington Post published the data on the 12 worst shootings in the U.S., following upon the Newtown massacre, I decided to plot the data cumulatively. The acceleration in deaths shown by graphing the data this way is breath-taking, and probably the scariest data I've ever plotted in this format.
Some would criticize it because it omits smaller incidents, or because of problems with selection of data, but the general outcome would hold up over a range of other criteria for data selection.
We'll have much more about this on the show tonight. For now, as Catania says, he's looking at just the effect of the 12 worst shootings -- he's not accounting for every shooting, every year. His chart is after the jump.
I added marks on the chart to account for the big jump in the last decade, from the shooting at Columbine High School in 1999 to the shooting at Virginia Tech in 2007. Following Virginia Tech, we had three of the deadliest shootings happen in one year, 2009, followed by two this year. Half the dozen worst shootings took place in half-century span. The other half happened in last half-decade.
UPDATE: I can see from the comments that the graph can be confusing at first glance. The numbers on the left are cumulative -- each mass killing is added to the one(s) before. As @Kate says below, the idea is to see the slope of the curve.