The figure below displays the number of mass shootings — incidents and victims — from 1976 through 2010. These reflect all mass shootings in which at least four victims were killed that had been reported to the FBI by local law enforcement authorities as part of the routine collection of crime statistics. Unlike the Mother Jones approach, these data do not exclude cases based on motive, location, or victim-offender relationship. They only exclude incidents in which fewer than four victims (other than the assailant) were killed, murders committed with a weapon other that a firearm, or isolated cases that may have occurred in jurisdictions that did not report homicide data to the FBI. Also, only because of the usual time lag in crime reporting, the figures for 2011 in 2012 are not yet available.
According to these expanded figures, there have been, on average, nearly 20 mass shootings a year in the United States. Most, of course, were nowhere as deadly as the recent massacres in Colorado and Connecticut that have countless Americans believing that a new epidemic is upon us and have encouraged healthy debate concerning causes and solutions. Notwithstanding the awful tragedies of this past year, there has been no upward trend in mass shootings.
What is abundantly clear from the full array of mass shootings, besides the lack of any trend upward or downward, is the largely random variability in the annual counts. There have been several points in time when journalists and other people have speculated about a possible epidemic in response to a flurry of high profile shootings. Yet these speculations have always proven to be incorrect when subsequent years reveal more moderate levels.
(Emphasis mine.) You mean Mother Jones picked their data to suit their narrative? Quel horreur! Via Mass shootings not trending – James Alan Fox – Crime & Punishment blog – Boston.com.